SERIES 


UC-NRLF 


*B    3m    fi3T 


if. 
l 

HHH 

U 

■ 


i  1  Q 


-«*\.    .*       lj    Irwij  3, 


EDITOR 


•_  Agric .  Educ  «  7nc.  J 


m*jM  u8sa; 


i  si 


Qbe  IRural  ftext^Boofe  Series 

Edited  by  L.  H.  BAILEY 


SOILS   AND   FERTILIZERS 


Etje  iftural  Eext^iSooft  Series 

Edited  by  L.  H.  BAILEY 
Carleton,  The  Small  Grains. 
B.    M.    Duggar,    Plant     Physiology,    with 

special  reference  to  Plant  Production. 
J.  F.  Duggar,   Southern  Field  Crops. 
Gay,  The  Breeds  of  Live-Stock. 
Gay,    The    Principles    and     Practice    of 

Judging  Live-Stock. 
Goff,    The    Principles   of    Plant    Culture, 

Revised. 
Harper,  Animal  Husbandry  for  Schools. 
Harris    and    Stewart,    The     Principles     of 

Agronomy. 
Hitchcock,  A  Text -Book  of  Grasses. 
Jeffery,  Text-Book  of  Land  Drainage. 
Jordan,  The   Feeding  of  Animals,  Revised. 
Livingston,  Field   Crop  Production. 
Lyon,  Soils  and  Fertilizers. 
Lyon,  Fippin   and    Buckman,  Soils  —  Their 

Properties  and   Management. 
Mann,  Beginnings   in  Agriculture. 
Montgomery,  The  Corn  Crops. 
Morgan,  Field  Crops  for  the  Cotton-Belt. 
Mumford,  The  Breeding  of  Animals. 
Piper,    Forage  Plants  and  their  Culture. 

Warren,  Elements  of  Agriculture. 

Warren,  Farm  Management. 

Wheeler,  Manures  and  Fertilizers. 

White,  Principles  of  Floriculture. 

Widtsoe,  Principles  of  Irrigation  Practice. 


Plate  I.     "The  earth  is  perhaps  a  stern  earth,  but  it  is  a  kindly 
earth."  —  Bailey. 


SOILS  AND  FERTILIZERS 


BY 


T.   LYTTLETON   LYON 

PROFESSOR    OP   SOIL   TECHNOLOGY   IN    THE    NEW    YORK 

STATE    COLLEGE    OF   AGRICULTURE    AT 

CORNELL    UNIVERSITY 


THE   MACMILLAN   COMPANY 

1921 

Ml  rights  reserved 


Copyright,  1917, 
By  THE  MACMILLAN  COMPANY. 


Set  up  and  elect rotyped.     Published  August,  191.7* 

■ 


Nortoootf  lPr«s 

J.  S.  Cushing  Co.  —  Berwick  &  Smith  Co* 

Norwood,  Mass.,  U.S.A. 


PREFACE 

In  many  of  the  high  schools  and  other  secondary  schools 
into  which  instruction  in  agriculture  was  introduced  a  few 
years  ago  there  has  been  such  a  development  of  the  subject 
that  one  general  text  is  no  longer  adequate.  In  these  schools 
some  of  the  more  important  phases  of  the  subject  now  re- 
ceive a  degree  of  attention  that  calls  for  specialized  texts. 
This  is  particularly  true  of  the  secondary  agricultural  schools 
and  the  normal  schools.  It  was  with  the  hope  of  meeting 
this  need,  and  also  of  contributing  to  the  demands  of  short 
courses  in  agriculture  and  of  summer  courses  for  teachers, 
that  this  book  was  written. 

The  attempt  has  been  made  so  to  present  the  subject  that 
the  pupil  who  has  no  knowledge  of  chemistry  or  other  natural 
science  will  be  able  to  understand  it.  No  chemical  symbols 
or  formulae  have  been  used.  Use  has  been  freely  made  of  a 
limited  number  of  names  of  chemical  substances  contained 
in  commercial  fertilizers  which  contribute  to  the  nutrition 
of  plants.  These,  however,  are  terms  with  which  the  pupil 
can  familiarize  himself  as  readily  as  with  the  geographical 
and  other  names  that  he  has  already  mastered. 

Following  each  chapter  are  field  and  laboratory  exercises, 
designed  to  illustrate  in  a  concrete  manner  the  teachings  of 
the  text.  There  are  more  of  these  than  any  one  teacher  will 
probably  find  it  expedient  to  have  his  class  perform,  but  the 
considerable  number  and  variety  of  exercises  will  make  it 
possible  for  any  school  to  afford  the  necessary  facilities  for 
performing  some  of  the  demonstrations. 

v 

451794 


VI  PREFACE 

It  has  not  been  thought  necessary  to  cite  authorities  on 
which  the  statements  in  the  text  are  based.  For  these  and 
for  more  complete  discussions  of  most  of  the  matters  treated 
in  this  book,  teachers  and  others  who  may  wish  to  pursue 
the  subject  further  are  referred  to  the  college  text  on  soils 
by  Lyon,  Fippin  and  Buckman. 

The  author  is  especially  indebted  to  Dr.  H.  O.  Buckman 
for  much  assistance  and  advice.  He  has  contributed  prac- 
tically all  of  the  laboratory  exercises. 

Ithaca,  N.  Y., 
June  1,  1917. 


CONTENTS 

CHAPTER   I 

PAQEB 

Soil  as  a  Medium  for  Plant  Growth        .         .         .  1-7 

Soil  as  a  mechanical  support  for  plants,  §  1 ;  Soil 
as  a  reservoir  for  water  needed  by  plants,  §  2 ;  Uses 
of  water  by  plants,  §  3 ;  Soil  as  a  source  of  plant-food 
materials,  §  4 ;  Quantities  of  plant-food  materials  in 
the  earth's  crust,  §  5 ;  Soil-forming  rocks,  §  6 ;  Rock- 
forming  minerals,  §  7  ;   Important  minerals,  §  8. 

Questions  on  Chapter  I      ......  7-8 

Laboratory  Exercises  .......  8-10 

Study  of  soil-forming  minerals,  I ;  Study  of  soil- 
forming  rocks,  II ;  To  show  that  plants  give  off 
water,  III;  Conditions  for  plant  growth,  IV;  Ef- 
fects of  different  plant  nutrients,  V. 

CHAPTER   II 

Soil  Formation  and  Transportation  .         .         .         11-16 

Agencies  concerned  in  soil  formation  and  trans- 
portation, §  9 ;  Action  of  heat  and  cold,  §  10 ;  Ac- 
tion of  frost,  §  11 ;  Action  of  water,  §  12  ;  Action  of 
ice,  §  13 ;  Action  of  wind,  §  14 ;  Action  of  gases, 
§  15 ;  Action  of  plants  and  animals,  §  16 ;  Powdered 
rock  is  not  soil,  §  17. 

Questions  on  Chapter  II •  16 

Laboratory  Exercises  .......  17 

Soil  formation  and  transportation,  I. 

CHAPTER   III 

Soil  Formations 18-28 

Residual  soils,  §  18 ;  Distribution  of  residual  soils, 
§19;    Cumulose  soils,   §20;    Colluvial  soils,   §21; 

vii 


Vlll  CONTENTS 

PAGES 

Alluvial  soils,  §  22 ;  Character  and  distribution  of 
alluvial  soils,  §  23 ;  Marine  soils,  §  24 ;  Distribution 
of  marine  soils,  §  25 ;  Lacustrine  soils,  §  26 ;  Glacial 
soils,  §  27 ;  ^Eolian  soils,  §  28. 

Questions  on  Chapter  III  .......  28 

Laboratory  Exercises  .......  29 

Classification  of  soils,  I ;  Use  of  soil  auger  in  taking 
samples,  II. 

CHAPTER   IV 

Texture  and  Structure  op  Soils  ....  30-45 
Shape  of  particles,  §  29 ;  Space  occupied  by  parti- 
cles, §  30 ;  Mechanical  analysis  of  soils,  §  31 ;  Me- 
chanical analysis  of  some  typical  soils,  §  32  ;  Soil  class, 
§  33 ;  Some  properties  of  the  separates,  §  34 ;  Chemi- 
cal composition  of  soil  separates,  §  35 ;  Soil  structure  . 
§  36 ;  Relation  of  structure  to  pore  space,  §  37 ;  Re- 
lation of  structure  to  tilth,  §  38 ;  Conditions  and 
operations  that  affect  structure,  §  39 ;  Relation  of 
texture  to  structure,  §  40 ;  Wetting  and  drying,  §  41 ; 
Freezing  and  thawing,  §  42 ;  Effect  of  organic  matter 
on  structure,  §  43 ;  Roots  and  animals,  §  44 ;  Tillage 
and  structure,  §  45 ;  Structure  as  affected  by  lime, 
§  46 ;  The  soil  survey,  §  47 ;  Classification  of  soils, 
§  48 ;    Information  furnished  by  a  soil  survey,  §  49. 

Questions  on  Chapter  IV  .         .         .         .         .         .         .  45 

Laboratory  Exercises 46-50 

Examination  of  soil  particles,  I ;  Examination  of 
soil  separates,  II ;  Simple  mechanical  analysis,  III ; 
Study  of  soil  class  and  its  determination  by  examina- 
tion, IV ;  Determination  of  soil  class  from  a  mechani- 
cal analysis,  V;  Soil  structure,  VI;  Determination 
of  apparent  specific  gravity  of  dry  sand  and  clay, 
VII ;  Calculation  of  pore  space,  VIII ;  A  study  of  the 
plow,  IX. 

CHAPTER  V 

Organic  Matter 51-57 

Classes  of  organic  matter,  §  50 ;  Beneficial  effects 
of  organic  matter,  §  51 ;  Porosity  of  organic  matter, 


CONTENTS  .  IX 


§  52 ;  Organic  matter  and  drainage,  §  53 ;  Organic 
matter  and  soil  color,  §  54 ;  Organic  matter  a  source 
of  plant-food  material,  §  55 ;  Organic  matter  and 
nitrogen,  §  56 ;  Organic  matter  and  soil  microorgan- 
isms, §  57 ;  Organic  matter  forms  acids,  §  58 ;  In- 
jurious effect  of  organic  matter,  §  59 ;  Management 
of  organic  matter  in  soils,  §  60 ;  Sources  of  organic 
matter,  §  61. 

Questions  on  Chapter  V     ......  57 

Laboratory  Exercises  .......'  58-60 

Examination  of  soil  —  organic  matter,  I ;  Exami- 
nation of  peat  and  muck,  II ;  Estimation  of  organic 
matter,  III;  Extraction  of  decomposed  organic 
matter,  IV ;  Influence  of  organic  matter  on  percola- 
tion through  soils,  V ;  Influence  of  organic  matter  on 
percentage  of  moisture  held  in  soil,  VI ;  Influence  of 
organic  matter  on  percentage  of  moisture  held  in  soil, 
VII. 

CHAPTER  VI 

Soil  Water 61-85 

Forms  of  water  in  soils,  §  62 ;  How  the  three  forms 
of  water  differ,  §  63 ;  Hygroscopic  water,  §  64 ;  Capil- 
lary water,  §  65 ;  Capillary  water  capacity,  §  66 ; 
Movement  of  capillary  water,  §  67 ;  Effect  of  tex- 
ture on  capillary  movement,  §  68 ;  Effect  of  struc- 
ture on  capillary  movement,  §  69 ;  Height  of  water 
column  and  capillary  movement,  §  70 ;  Gravitational 
water,  §  71 ;  The  water  table,  §  72  ;  Relations  of  soil 
water  to  plants,  §  73 ;  Ways  in  which  water  is  useful 
to  plants,  §  74 ;  Water  requirements  of  plants,  §  75 ; 
Transpiration  by  different  crops,  §  76 ;  Effect  of 
moisture  on  transpiration,  §  77 ;  Effect  of  humidity, 
wind  and  temperature  of  the  air,  §  78 ;  Effect  of  soil 
fertility  on  transpiration,  §  79 ;  Quantity  of  water 
required  to  mature  a  crop,  §  80 ;  Capillary  move- 
ment and  plant  requirement,  §  81 ;  Optimum  mois- 
ture for  plant  growth,  §  82 ;  The  control  of  soil  mois- 
ture, §  83;   Run-off,  §  84;   Percolation,  §  85;  Evap- 


X  CONTENTS 

PAGES 

oration,  §  86;  Mulches  for  moisture  control,  §  87; 
The  soil  mulch,  §  88 ;  Frequency  of  stirring,  §  89 ; 
Depth  of  mulch,  §  90 ;  Effectiveness  of  mulches, 
§  91 ;  Other  devices  to  prevent  evaporation,  §  92 ; 
Rolling  and  subsurface  packing,  §  93 ;  Removal  of 
water  by  drainage,  §  94 ;  Benefits  of  drainage,  §  95 ; 
Soil  air,  §  96 ;  Soil  tilth,  §  97 ;  Available  water  dur- 
ing the  growing  season,  §  98 ;  Length  of  growing 
season,  §  99 ;  Other  results  of  drainage,  §  100 ;  Open 
ditches,  §  101 ;  Tile  drains,  §  102 ;  Arrangement  of 
drains,  §  103 ;  Digging  ditches  and  laying  tile,  §  104. 

Questions  on  Chapter  VI  .......  85 

Laboratory  Exercises 85-89 

Determination  of  the  percentage  of  water  in  a  soil, 
I ;  Capillary  movement  in  different  soils,  II ;  Rate 
of  percolation  of  water  through  soils,  III;  Water- 
holding  capacity  of  soils,  IV ;  Moisture  conservation 
by  means  of  a  soil  mulch,  V ;  Loss  of  water  by  tran- 
spiration, VI ;  Review  problems  Chapter  IV  and  VI, 
VII;  Tile  drainage,  VIII. 


CHAPTER  VII 

Plant-Food  Materials  in  Soils  .         .         .         .       90-110 

Variations  in  content  of  plant  nutrients  in  different 
soils,  §  105 ;  The  total  supply  of  plant-food  materials, 
§  106;  Upward  movement  of  plant-food  materials, 
§  107 ;  Plant  nutrients  compose  a  small  part  of  the 
soil,  §  108;  Relation  of  composition  to  productive- 
ness, §  109 ;  Available  and  unavailable  plant-food 
materials,  §  110;  Conditions  that  influence  avail- 
ability, §  111;  Water-soluble  matter  in  soil,  §  112; 
Relation  of  water-soluble  matter  to  productiveness, 
§  113;  Chemical  analysis  of  soil,  §  114;  Absorptive 
properties  of  soils,  §  115 ;  Selective  absorption,  §  116 ; 
The  availability  of  absorbed  fertilizers,  §  117 ;  Other 
forms  of  available  plant-food  material  in  soils,  §  118; 
Loss  of  plant-food  material  in  drainage  water,  §  119; 


CONTENTS 


XI 


Quantities  of  plant-food  materials  in  drainage,  §  120 ; 
Effect  of  crop  growth  on  loss  of  plant  nutrients  in 
drainage,  §  121 ;  Effect  of  fertilizers  on  loss  of  plant- 
food  materials  in  drainage,  §  122;  Drainage  water 
from  different  soils,  §  123 ;  Absorption  of  good  mate- 
rials by  plants,  §  124 ;  How  plants  absorb  nutrients, 
§  125;  How  roots  aid  in  solution  of  soil,  §  126;  Pro- 
duction of  carbon  dioxide  by  microorganisms,  §  127 ; 
Solvent  action  of  roots  in  other  ways,  §  128 ;  Differ- 
ence in  absorptive  power  of  crops,  §  129 ;  Substances 
needed  by  plants  and  substances  merely  absorbed, 
§  130;  Quantities  of  plant-food  materials  removed 
by  crops,  §  131 ;  Possible  exhaustion  of  mineral 
nutrients,  §  132. 

Questions  on  Chapter  VII  ...... 

Laboratory  Exercises  ....... 

Soluble  matter  of  soil,  I ;  Absorptive  power  of  soil 
for  dyes,  II ;  Selective  absorption  by  soil,  III ;  Ab- 
sorptive power  of  the  soil  for  gas,  IV. 


110-111 
111 


CHAPTER   VIII 

Acid  Soils  and  Alkali  Soils  .  .  .  .  . 
Nature  of  soil  acidity,  §  133;  Positive  acidity, 
§  134 ;  Negative  acidity,  §  135 ;  Ways  by  which  soils 
become  sour,  §  136 ;  Drainage  as  a  cause  of  acidity, 
§  137 ;  Effect  of  plant  growth  on  soil  acidity,  §  138 ; 
Effect  of  fertilizers  on  soil  acidity,  §  139 ;  Effect  of 
green-manures  on  acidity,  §  140 ;  Weeds  that  flourish 
on  sour  soils,  §  141 ;  Crops  adapted  to  sour  soils, 
§  142 ;  Crops  that  are  injured  by  acid  soils,  §  143 ; 
Litmus  paper  test  for  soil  acidity,  §  144;  Litmus 
paper  and  potassium  nitrate,  §  145 ;  The  Truog  test, 
§  146;  Alkali  soils,  §  147;  Nature  and  movements 
of  alkali,  §  148 ;  Effect  of  alkali  on  crops,  §  149 ; 
Tolerance  of  different  plants  to  alkali,  §  150 ;  Irriga- 
tion and  alkali,  §  151 ;  Removal  of  alkali,  §  152 ; 
Control  of  alkali,  §  153. 


112-121 


Questions  on  Chapter  VIII 


121-122 


Xll 


CONTENTS 


Laboratory  Exercises  .         .         .         . 

Acid  soils  in  the  field,  I ;  Litmus  paper  with  and 
without  potassium  nitrate,  II ;  Litmus  paper  test, 
III ;  Test  for  soil  carbonates,  IV ;  Ammonia  test  for 
acidity,  V ;  Zinc  sulfide  test  for  acidity,  VI ;  Incrusta- 
tion of  "alkali"  by  capillary  action,  VII. 


PAGES 

122-124 


CHAPTER   IX 

The  Germ  Life  of  the  Soil 125-140 

Microorganisms  injurious  to  crops,  §  154 ;    Germs 
not  directly  injurious  to  crops,  §  155  ;    Numbers  of 
bacteria  in  soils,  §  156 ;  Conditions  affecting  bacterial 
growth,  §  157 ;   Air  supply,  §  158 ;   Moisture,  §  159 ; 
Temperature,   §  160 ;    Organic  matter,    §  161 ;    Soil 
acidity,  §  162 ;    Bacteria  in  relation  to  soil  fertility, 
§  163 ;    Action  on  mineral  matter,   §  164 ;    Decom- 
position of  non-nitrogenous  organic  matter,   §  165; 
Decomposition  of  nitrogenous  organic  matter,  §  166 ; 
Ammonification,  §  167;  Nitrification,  §  168;  Effect 
of  soil  aeration  on  nitrate  formation,  §  169 ;  Effect  of 
temperature  on  nitrate  formation,  §  170;  Effect  of 
sod  on  nitrate  formation,  §  171 ;    Depths  at  which 
nitrate  formation  takes  place,  §  172  ;  Loss  of  nitrates 
in  drainage,  §  173 ;   Denitrification,  §  174 ;  Nitrogen 
fixation,  §  175 ;  Nitrogen  fixation  through  symbiosis 
with  higher  plants,   §  176;    Soil  inoculation  for  le- 
gumes,   §  177;     Nitrogen     fixation     by    free-living 
germs,  §  178. 
Questions  on  Chapter  IX  ......  40 

Laboratory  Exercises  .         .         .         .         .         .         .     140-142 

Test  for  nitrates  in  soil,  I ;  Test  for  ammonia  in 
soil,  II ;  Factors  affecting  nitrate  formation,  III ; 
Examination  of  legume  nodules,  IV ;  Examination  of 
nodule  bacteria,  V;    Soil  inoculation,  VI. 

CHAPTER   X 

Soil  Air  and  Soil  Temperature  ....     143-152 

Soil  air  contained  largely  in  non-capillary  spaces, 
§  179 ;   There  may  be  too  much  or  too  little  soil  air, 


CONTENTS 


Xlll 


§  180 ;  Movement  of  soil  air,  §  181 ;  Movement  of 
water,  §  182 ;  Diffusion  of  gases,  §  183 ;  Composi- 
tion of  soil  air,  §  184 ;  Production  of  carbon  dioxide 
in  soils,  §  185 ;  Conditions  that  affect  the  quantity 
of  carbon  dioxide  in  soils,  §  186 ;  Usefulness  of  air  in 
soils,  §  187;  Oxygen,  §  188;  Nitrogen,  §  189;  Car- 
bon dioxide,  §  190 ;  Control  of  the  volume  and  move- 
ment of  soil  air,  §  191;  Soil  temperature,  §  192; 
Sources  of  soil  heat,  §  193 ;  Relation  of  soil  tempera- 
ture to  atmospheric  temperature,  §  194 ;  Factors  that 
modify  soil  temperature,  §  195 ;  Control  of  soil  tem- 
perature, §  196. 

Questions  on  Chapter  X     ...... 

Laboratory  Exercises  ....... 

Movement  of  soil  air  as  measured  by  texture  and 
structure,  I ;  The  presence  of  carbon  dioxide  in  soil 
air,  II ;  Production  of  carbon  dioxide  by  germs,  III ; 
Temperature  and  soil  color,  IV ;  Slope  and  soil  tem- 
perature, V;    Drainage  and  temperature,  VI. 


152 
152-154 


CHAPTER   XI 

Nitrogenous  Fertilizers 

Relative  quantities  of  the  different  forms  of  nitro- 
gen in  soils,  §  197 ;  Forms  in  which  nitrogen  is  ab- 
sorbed by  plants,  §  198 ;  Nitrates  as  plant-food 
materials,  §  199;  Absorption  of  ammonia  by  agri- 
cultural plants,  §  200 ;  Direct  utilization  of  organic 
nitrogen  by  crops,  §  201 ;  Forms  of  nitrogen  in  fer- 
tilizers, §  202 ;  Nitrate  of  soda,  §  203  ;  Crops  mark- 
edly benefited,  §  204 ;  Effect  of  nitrate  of  soda  on  soils, 
§  205 ;  Sulfate  of  ammonia,  §  206 ;  Composition  of 
sulfate  of  ammonia,  §  207 ;  Action  when  applied  to 
soils,  §  208;  Cyanamid,  §  209;  Composition  of 
cyanamid,  §  210;  Changes  in  the  soil,  §  211;  Fer- 
tilizers containing  organic  nitrogen,  §  212;  Vege- 
table products,  §  213;  Animal  products,  §  214;  Fish 
waste,  §  215;  Guano,  §  216;  Effects  of  nitrogen  on 
plant   growth,    §  217 ;    Availability   of   nitrogenous 


155-168 


XIV 


CONTENTS 


fertilizers,   §  218 ;    Relative  values  of  organic  and 
inorganic  nitrogenous  fertilizers,  §  219. 

Questions  on  Chapter  XI  ....... 

Laboratory  Exercises  ....... 

Influence  of  nitrogen  on  plant  growth,  I ;  Exami- 
nation and  identification  of  nitrogen  fertilizers,  II; 
Comparison  of  fertilizer  effects  on  plant  growth,  III. 


168 
168-170 


CHAPTER  XII 

Phosphoric  Acid  Fertilizers 171-176 

Bone  phosphate,  §  220;  Mineral  phosphates, 
§  221 ;  Basic  slag,  §  222 ;  Acid  phosphate,  §  223 ;  Com- 
position of  acid  phosphate,  §  224 ;  Reverted  phos- 
phoric acid,  §,225;  Absorption  of  acid  phosphate  by 
soil,  §  226 ;  Relative  availability  of  phosphoric  acid 
fertilizers,  §  227 ;  Rock  phosphate  versus  acid  phos- 
phate, §  228 ;  Effect  of  phosphoric  acid  on  plant 
growth,  §  229 ;  Plants  particularly  benefited  by 
phosphoric  acid,  §  230. 

Questions  on  Chapter  XII 176-177 

Laboratory  Exercises  .......     177-178 

Influence  of  phosphoric  acid  on  plant  growth,  I; 
Examination  and  identification  of  phosphate  fer- 
tilizers, II;  Comparison  of  fertilizer  effects  on 
plant  growth,  III. 


CHAPTER  XIII 

Potash  and  Sulfur  Fertilizers 

Stassfurt  salts,  §  231 ;  Wood  ashes,  §  232 ;  Insolu- 
ble potash  fertilizers,  §  233 ;  Effects  of  potash  on 
plant  growth,  §  234 ;  Sulfur  as  a  fertilizer,  §  235 ; 
Experiments  with  sulfur  as  a  fertilizer,  §  236 ; 
Quantities  of  sulfur  contained  in  crops,  §  237 ; 
Quantities  of  sulfur  in  soils,  §  238 ;  Quantities  of  sul- 
fur in  drainage  water,  §  239 ;  Sulfur  contained  in  fer- 
tilizers, §  240. 


179-185 


CONTENTS 


XV 


Questions  on  Chapter  XIII        ...... 

Laboratory  Exercises  ....... 

Influence  of  potash  on  plant  growth,  I ;  Examina- 
tion and  identification  of  potash  fertilizers  and  sulfur, 
II ;  Comparison  of  fertilizer  effects  on  plant  growth, 
III. 


185 
185-186 


CHAPTER  XIV 


Lime 


Forms  of  lime,  §  241 ;  Absorption  of  lime  by  soils, 
§  242 ;  Lime  requirement  of  soils,  §  243 ;  Effect  of 
lime  on  tilth,  §  244 ;  Effect  of  lime  on  bacterial 
action,  §  245 ;  Liberation  of  plant-food  materials, 
§  246 ;  Effect  on  plant  diseases,  §  247 ;  The  use  of 
magnesian  limes,  §  248 ;  Caustic  lime  versus  ground 
limestone,  §  249 ;  Fineness  of  grinding  limestone, 
§  250;    Gypsum  or  land  plaster,  §  251. 

Questions  on  Chapter  XIV 

Laboratory  Exercises  ....... 

A  study  of  the  forms  of  lime,  I ;  Fineness  of 
ground  limestone,  II ;  Effect  of  lime  on  biological 
action,  III;  Flocculation  by  lime,  IV;  Flocculation 
by  lime,  V ;  Lime  and  the  rotation,  VI ;  Forms  of 
lime  to  apply,  VII. 


187-192 


192 
193-195 


CHAPTER   XV 

The  Purchase  and  Mixing  of  Fertilizers 

Brands  of  fertilizers,  §  252 ;  High-  and  low-grade 
fertilizers,  §  253 ;  Fertilizer  inspection  and  control, 
§  254  ;  Trade  values  of  fertilizer  ingredients,  §  255  ; 
Computation  of  the  wholesale  value  of  a  fertilizer, 
§  256 ;  Home  mixing  of  fertilizers,  §  257 ;  Fertilizers 
that  should  not  be  mixed,  §  258 ;  Calculation  of  a 
fertilizer  mixture,  §  259 ;  How  to  mix  the  ingredients, 
§  260. 


196-205 


Questions  on  Chapter  XV 


205-206 


XVI 


CONTENTS 


Laboratory  Exercises 

Fertilizer  inspection  and  control,  I ;  Laboratory 
mixture  of  fertilizers,  II ;  Home  mixture  of  fertilizers, 
III. 

CHAPTER   XVI 

The  Use  of  Fertilizers 

Fertilizers  for  different  crops,  §  261 ;  Small  grains, 
§  262 ;  Grass  crops,  §  263  ;  Leguminous  crops,  §  264 ; 
Root  crops,  §  265 ;  Vegetables,  §  266 ;  Orchards, 
§  267 ;  Fertilizer  mixtures  for  different  crops, 
§  268 ;  Fertilizers  for  different  soils,  §  269  ;  Calcula- 
tion of  results  of  fertilizer  experiments,  §  270 ;  Fer- 
tilizing the  rotation,  §  271 ;  Methods  of  applying  fer- 
tilizers, §  272 ;  The  limiting  factor,  §  273  ;  The  law 
of  diminishing  returns,  §  274 ;  Conditions  that  influ- 
ence the  effect  of  fertilizers,  §  275 ;  Response  of  sandy 
and  of  clay  soils  to  fertilizers,  §  276 ;  Cumulative 
need  of  fertilizers,  §  277. 

Questions  on  Chapter  XVI         ...... 

Laboratory  Exercises  ....... 

Fertilization  of  standard  rotations,  I;  Fertiliza- 
tion of  home-farms,  II ;  Fertilizer  practice  in  the 
community,  III;   Fertilizer  experimentation,  IV. 


PAGE3 

206 


207-219 


219 
219-220 


CHAPTER  XVII 

Farm  Manures 

Solid  and  liquid  manure,  §  278 ;  Chemical  compo- 
sition of  manures,  §  279 ;  Farm  manure  an  unbal- 
anced fertilizer,  §  280 ;  Quantities  of  manure  voided 
by  animals,  §  281 ;  Effect  of  food  on  composition  of 
manure,  §  282 ;  Commercial  evaluation  of  manures, 
§  283 ;  Agricultural  evaluation  of  manures,  §  284 ; 
Deterioration  of  farm  manure,  §  285 ;  Fermentations 
of  manure,  §  286 ;  Leaching  of  farm  manure,  §  287 ; 
Protected  manure  more  effective,  §  288 ;  Reinforcing 
manure,  §  289 ;  Methods  of  handling  manure,  §  290  ; 
Covered  barnyard,  §  291 ;   Application  of  manure  to 


221-232 


CONTENTS 


XVll 


land,  §  292 ;   Place  of  farm  manure  in  crop  rotation, 
§293. 

Questions  on  Chapter  XVII       .         .         .         .         . 

Laboratory  Exercises  ....... 

Study  of  farm  manure,  I ;  Experiments  with  farm 
manure,  II ;  The  value  of  manure  produced  on  the 
home  farm,  III ;  Reinforcement  of  farm  manure, 
IV;    Building  of  a  compost  pile,  V. 


232 
233-234 


CHAPTER   XVIII 

Green-Manures 235-240 

Protective  action  of  green  manures,  294;  Mate- 
rials supplied  by  green  manures,  §  295 ;  Transfer  of 
plant-food  materials,  §  296 ;  Crops  used  for  green- 
manuring,  §  297 ;  When  green-manures  may  be  used, 
§  298 ;    Handling  green-manure  crops,  §  299 


Questions  on  Chapter  XVIII     . 
Laboratory  Exercises  .... 

Study  of  green-manure  in  the  field, 
manure  and  the  rotation,  II. 


I ;    Green- 


240 
240-241 


CHAPTER   XIX 

Crop  Rotation,       ........ 

Crop  rotation  and  soil  productiveness,  §  300 ; 
Root  systems  of  different  crops,  §  301 ;  Nutrients  re- 
moved from  soil  by  different  crops,  §  202 ;  Some 
crops  or  crop  treatments  prepare  nutriment  for 
other  crops,  §  303 ;  Crops  differ  in  effect  on  soil 
structure,  §  304 ;  Certain  crops  check  certain  weeds, 
§  305 ;  Plant  diseases  and  insects,  §  306 ;  Loss  of 
plant-food  material  between  crops,  §  307 ;  Produc- 
tion of  toxic  substances  from  plants,  §  308 ;  Manage- 
ment of  a  crop  rotation,  §  309 


Questions  on  Chapter  XIX         .... 
Laboratory  Exercises  ..... 

Crop  rotations,  I ;  Fertilizing  the  rotation, 


242-247 


248 
248 


II. 


LIST   OF   ILLUSTRATIONS 


facing 
facing 
facing 
facing 
facing 


facing 


Frontispiece 

Rock  disintegration  by  heat  and  cold 

Wearing  action  of  water  on  rock 

Plants  as  soil  formers 

Glacial  soil  and  alluvial  soil     . 

Stratification  of  rock  and  soil 

Auger  for  taking  soil  samples 

Relative  sizes  of  soil  particles 

Graphic  statement  of  mechanical  analyses  of  soils  . 

Scheme  for  determining  soil  class  (after  Whitney)  . 

Ideal  arrangement  of  soil  particles  .... 

Section  showing  structure  of  loam  soil  in  good  tilth 

Plowed  land,  showing  good  and  poor  tilth 

Apparatus  for  simple  mechanical  analysis  of  soil     . 

Apparatus  for   the   determination   of  the   apparent   specific 

gravity  of  soil 

A  walking  plow  and  its  attachments 
Cross  sections  of  furrows  turned  at  different  angles 
Apparatus  for  the  estimation  of  organic  matter  in  soil 
Apparatus  for  estimating  rate  of  percolation  and  water-holding 

capacity 

Soil  particles  and  surrounding  films  of  hygroscopic  and  capil 

lary  water 

Erosion  of  soil  by  water  and  by  wind      .         .         .        facing 
Section  of  soil  with  and  without  a  mulch 
Systems  of  laying  out  tile  drains     . 

Drain  tile  outlets facing 

Sections  of  land  showing  locations  of  tile  drains  and  water 

.  tables 

Diagrammatic  explanation  of  water  control  in  a  humid  region 
Apparatus  for  moisture  measurement  .  .  .  facing 
Apparatus  for  demonstration  of  effectiveness  of  mulches  in 

conserving  soil  water 

Apparatus  for  observation  of  transpiration  of  water  from 

*  plants 

xix 


6 
12 
16 
25 
29 
29 
31 
33 
35 
38 
39 
42 
47 

49 
50 
56 
58 

59 

63 

72 
77 
82 
83 

84 
84 
86 

87 

88 


XX  LIST  OF  ILLUSTRATIONS 

PAGE 

Surface  soil  and  subsoil facing  92 

Relative   quantities   of  potash,   lime,   phosphoric   acid   and 

nitrogen  in  a  soil      ........  94 

Equipment  for  making  the  litmus  paper  test  ....  123 

Apparatus  for  making  the  zinc  sulfide  test      ....  124 

Relative  sizes  of  bacteria  and  soil  particles      .         .         .         .  128 

Appearance  of  some  soil  bacteria  (after  Lohnis)       .         .         .  131 

Diagrammatic  representation  of  the  nitrogen  cycle          .         .  139 
Apparatus  for  estimating  the  relative  rate  of  air  movement 

through  soils 153 

Apparatus  to  demonstrate  the  presence  of  carbon  dioxide  in 

soil  air      ..........  153 

Apparatus  to  demonstrate  the  formation  of  carbon  dioxide  in 

soil 154 

Effect  of  certain  fertilizer  constituents  on  plant  growth  facing  156 

Extent  to  which  fertilizers  are  used  in  the  several  states          .  197 

Tag  representative  of  the  kind  often  used  on  bags  of  fertilizer  201 

Plan  for  fertilizer  experiments 212 

Field  plat  experiments facing  212 

Influence  of  soil  moisture  on  the  effectiveness  of  fertilizers 

facing  218 

Composition  of  farm  manure 223 

Storage  of  farm  manure facing  226 

Movements  of  plant-food  materials  between  soil,  air  and  plant  237 

Cover  crops  which  are  also  green  manures       .         .        facing  238 


SOILS   AND   FERTILIZERS 


SOILS   AM)   FERTILIZERS 

CHAPTER  I 

SOIL  AS  A   MEDIUM  FOR  PLANT  GROWTH 

The  farmer's  interest  in  the  soil  is  due  chiefly  to  what 
it  contributes  to  plant  production.  In  this  respect  it  per- 
forms several  functions  :  (1)  it  acts  as  a  mechanical  support 
for  plants  by  furnishing  a  foothold  comprising  many  open- 
ings through  which  plant  roots  ramify  and  hold  the  plant 
in  place;  (2)  it-  serves  as  a  receptacle  in  which  water  is 
held  in  a  convenient  way  for  roots  to  appropriate ;  (3)  it  is 
composed,  in  part,  of  substances  that  dissolve  in  the  water 
which  it  holds  and  are  absorbed  from  solution  by  roots,  and 
utilized  by  plants  as  food  material ;  (4)  its  porous  nature 
allows  air  to  circulate  within  it,  thus  supplying  plant  roots 
witl),  air. 

These  are  the  contributions  that  soils  make  to  plant  growth. 
Before  proceeding  with  a  more  detailed  study  of  soil  it  will 
be  desirable  to  consider  briefly  the  needs  of  the  plant  as 
supplied  by  the  soil. 

1.  Soil  as  a  mechanical  support  for  plants.  —  Land  plants 
need  anchorage,  for  they  must  have  some  permanent  supply 
of  water  and  other  food  material,  which  is  not  to  be  had 
from  the  atmosphere.  The  soil  serves,  at  once,  as  anchor- 
age and  food  reservoir.  One  property  of  soil  that  adapts 
b  1      ' 


2  SOILS  AND  FERTILIZERS 

it  especially  for  the  growth  of  roots  is  its  permeable  structure, 
which  furnishes  innumerable  channels  through  which  roots 
may  ramify ;  another  property  is  its  compressibility,  which 
makes  it  possible  for  the  roots  to  grow  in  thickness  by 
forcing  together  the  surrounding  particles.  The  compacting 
thus  effected  may  be  noted  in  a  field  of  mangels  or  other 
large  roots  at  harvest.  The  firmness  of  this  anchorage  is 
illustrated  by  the  resistance  that  large  trees  offer  to  heavy 
winds. 

2.  Soil  as  a  reservoir  for  water  needed  by  plants.  —  The 
leaves  of  land  plants  thrive  without  being  in  contact  with 
water,  but  their  roots  must  have  a  nearly  constant  supply. 
This  the  soil  helps  to  maintain  by  catching  and  holding  more 
or  less  of  the  water  that  falls  as  rain.  The  water  thus  held 
is  in  contact  with  the  small  roots  and  root-hairs  of  plants, 
and  may  readily  be  absorbed  by  them. 

3.  Uses  of  water  by  plants.  —  Plants  require  moisture  for 
several  reasons :  (1)  Water  acts  as  a  solvent  for  substances 
that  are  essential  to  plant  growth,  and  these  substances  can 
be  absorbed  by  plants  only  when  they  are  in  solution. 
(2)  Water  is  itself  a  plant-food  material  and  it  either  becomes 
a  part  of  the  cell  without  change,  or  is  decomposed  and  its 
component  parts  are  used  in  forming  new  substances.  (3)  The 
cells,  of  which  plants  are  composed,  are  kept  filled  and  the 
plant  is  more  or  less  firm  and  erect  when  its  cells  are  extended 
with  water.  When  not  so  filled,  the  plant  wilts.  (4)  Nutri- 
tive substances  and  substances  formed  from  them  in  the 
plant  tissues  are  transferred  from  one  part  of  the  plant  to 
another,  as  occasion  requires,  by  water  in  the  plant.  (5)  The 
evaporation  of  moisture  from  leaves  (transpiration)  causes  a 
reduction  of  temperature  in  plants,  as  does  evaporation  of 
perspiration  from  animals. 

4.  Soil  as  a  source  of  plant-food  materials.  —  Plants  re- 
quire for  their  growth  certain  nutrient  substances,  of  which 


SOIL  AS  A   MEDIUM  FOR  PLANT  GROWTH          3 

some  are  derived  from  the  air  and  some  from  water,  but 
the  larger  number  must  be  obtained  from  soil.  They  may 
be  classified  thus : 

Substances  obtained  from  air  or  water : 

Carbon  Hydrogen 

Oxygen  Nitrogen 

Substances  obtained  from  soil : 
Nitrogen 

Phosphoric  acid  [phosphorus]  * 
Potash  [potassium] 
Lime  [calcium] 
Magnesia  [magnesium] 
Iron 
Sulfur 

All  these  substances  are  essential  to  the  normal  devel- 
opment of  farm  crops.  Carbon,  oxygen  and  nitrogen  are 
found  in  air.  Hydrogen  and  oxygen  are  in  water.  Plants 
obtain  their  carbon  from  the  air;  their  oxygen  from 
both  air  and  water;  their  hydrogen  from  water;  their  ni- 
trogen, in  the  case  of  certain  plants  only,  from  the  air.  The 
other  substances  are  found  in  all  arable  soils,  from  which 
plants  obtain  them  after  they  have  become  dissolved  in  the 
soil  water.  While  arable  soils  contain  all  these  substances, 
the  fact  that  they  must  be  in  solution  before  plants  can  use 

1  This  list  of  plant-food  materials  gives  the  names  commonly  used. 
Thus  the  terms  phosphoric  acid,  potash,  and  lime  are  the  ones  used  in  con- 
nection with  fertilizers.  Nitrogen  is  sometimes  spoken  of  as  ammonia  by 
fertilizer  manufacturers,  but  the  most  general  term  is  nitrogen.  The  words 
in  brackets  following  the  unbracketed  words  indicate  other  names  some- 
times found,  but  not  used  in  this  book. 

All  the  substances  in  this  list  are  capable  of  uniting  with  certain  other 
substances  to  form  various  combinations.  When  present  in  the  soil  they  are 
not  likely  to  be  in  the  same  combinations  as  when  present  in  plants.  When, 
therefore,  phosphoric  acid  in  soil  or  in  a  plant  is  spoken  of,  nothing  is  implied 
regarding  the  form  in  which  it  exists. 


4  SOILS  AND  FERTILIZERS 

them  sometimes  leads  to  a  deficiency  in  the  available 
supply.  This  is  either  because  they  are  not  present  in 
sufficient  quantity,  or  because  they  are  not  readily  dissolved 
by  the  liquids  with  which  they  come  in  contact.  Many 
things  tend  to  influence  the  quantity  of  these  substances 
that  plants  may  obtain.  Among  these  are  tillage,  decaying 
vegetation,  drainage  and  the  kind  of  plant  grown.  It  is 
the  nitrogen,  phosphoric  acid,  potash  and  possibly  sulfur 
that  are  most  likely  to  be  deficient  in  the  solution  to  which 
plants  have  access,  and  commercial  fertilizers  usually  con- 
tain one  or  more  of  these  substances. 

The  kind  of  fertilizer  that  it  will  be  desirable  to  apply 
depends,  in  part,  on  the  so-called  availability  of  each  of 
the  nutrient  substances  contained  in  the  soil,  availability  in 
this  case  meaning  the  readiness  with  which  the  plant  can 
appropriate  these  food  materials.  But  some  plants  require 
more  of  certain  of  these  substances  than  they  do  of  others. 
Hence  the  needs  of  the  plant  must  also  be  taken  into  con- 
sideration in  deciding  what  fertilizer  to  use  on  a  given  soil. 

5.  Quantities  of  plant-food  materials  in  the  earth's  crust. 
—  As  all  of  the  food  materials  that  plants  draw  from  soil, 
with  the  exception  of  nitrogen,  came  originally  from  rocks, 
it  is  of  some  interest  to  know  what  the  proportions  of  these 
substances  are  in  the  entire  crust  of  the  earth.  As  stated 
by  Clarke  they  are  present  in  the  following  percentages  : 

Oxygen 47.17  Potash .  3.00 

Iron    ........  4.44  Sulfur 0.11 

Lime        4.79  Phosphoric  acid   ....  0.25 

Magnesia 3.76 

Nitrogen  does  not  appear  in  this  list  because  it  does  not 
occur  as  a  constituent  of  the  rocks  forming  the  earth's  crust. 
The  nitrogen  that  soil  contains  is  derived  from  the  atmos- 
phere by  processes  that  will  be  described  later.  Most  of 
the  constituents  of  soil  have,  however,  been  formed  from 


SOIL  AS  A   MEDIUM  FOR  PLANT  GROWTH  5 

rock,  and  hence  soil  may  be  expected  to  have  a  somewhat 
similar  composition  to  that  of  the  earth's  crust. 

It  will  be  seen  that  two  of  the  important  nutrients,  as  far 
as  plants  are  concerned,  namely  phosphoric  acid  and  sulfur, 
are  present  in  relatively  small  quantities.  Potash,  magnesia, 
lime  and  iron  are  present  in  much  larger  proportions.  This 
is  somewhat  the  relation  in  which  we  are  likely  to  find  them 
in  soils,  and  emphasizes  the  probable  need  of  phosphoric 
acid  and  sometimes  sulfur  for  the  maximum  production  of 
crops.  Potash,  in  spite  of  its  greater  quantity,  is  often  not 
available  in  sufficient  amount  and  must  be  applied  as  a 
soluble  fertilizer. 

Lime,  being  easily  soluble  in  soil  water,  has  frequently 
been  leached  out  of  soils  in  such  quantities  that  it  must 
be  replaced.  Magnesia  is  less  soluble  and  hence  is  rarely 
lacking. 

6.  Soil-forming  rocks.  —  As  the  earth,  which  was  once 
a  molten  mass,  cooled,  the  crust  became  solid  and  this  solidi- 
fied material  formed  igneous  rocks,  so  called  to  distinguish 
them  from  rocks  that  were  formed  in  other  ways.  Some 
examples  of  igneous  rocks  are  granite,  syenite  and  basalt. 
Other  kinds  of  rocks,  called  sedimentary,  have  been  formed 
from  material  derived  from  igneous  rock  by  solution  and 
sedimentation,  and  later  solidified  into  rock,  often  under 
pressure.  Limestone,  dolomite,  shale  and  sandstone  repre- 
sent some  rocks  of  sedimentary  origin.  The  first  two  are 
quite  readily  soluble  in  soil  water,  having  been  deposited 
from  solution  in  the  process  of  their  formation.  Shale 
is  a  more  or  less  hardened  clay.  Sandstone,  as  its  name 
implies,  consists  of  sand  grains  cemented  together. 

Metamorphic  rocks  have  been  formed  by  heat,  pressure, 
solution  and  other  processes  acting  on  either  igneous  or  sedi- 
mentary rocks.  These  forces  have  frequently  produced 
rocks  quite  unlike  those  originally  involved  in  the  process. 


6  SOILS  AND,  FERTILIZERS 

Gneiss,  marble  and  slate  are  among  the  rocks  so  formed. 
Gneiss  somewhat  resembles  granite,  from  which  it  is 
formed,  but  unlike  granite  has  a  layered  structure,  the 
result  of  the  pressure  to  which  it  was  subjected.  Marble 
has  been  formed  from  limestone  or  dolomite  by  heat  and 
pressure,  which  have  caused  crystallization.  It  is  not, 
therefore,  so  readily  soluble  as  limestone.  Slate  has  been 
formed  from  shale  by  heat  and  pressure. 

7.  Rock-forming  minerals.  —  Most  rocks  are  not  homo- 
geneous, but  are  made  up  of  a  number  of  different  materials. 
An  examination  will  frequently  show  grains  of  different 
sizes,  colors  and  hardness.  The  grains  are  minerals  and 
they  differ  from  each  other  in  their  composition  as  they 
do  in  their  appearance.  But  each  mineral  always  has  a 
more  or  less  well-defined  composition,  so  that  when  we  have 
a  certain  mineral  we  know  something  of  the  quantity  of 
potash  or  lime  or  other  base  that  it  contains.  The  quan- 
tity of  potash  or  other  plant-food  material  in  a  rock  will 
depend  on  the  proportion  of  minerals  containing  those  sub- 
stances that  compose  the  rock. 

8.  Important  minerals.  —  There  are  a  few  minerals  that 
it  will  be  well  to  mention  :  (1)  because  they  or  their  products 
occur  in  very  large  quantity  in  soil  and  influence  its  physical 
properties;  (2)  because  of  the  plant-food  material  that 
they  contain.  Quartz  and  feldspar  are  examples  of  the  class 
first  mentioned.  Quartz  is  found  in  almost  all  soils,  and 
may  form  from  85  to  99  per  cent  of  their  composition.  It 
is  particularly  prevalent  in  sandy  soils.  It  usually  occurs 
as  a  large  grain,  called  sand,  is  hard  and  insoluble  and  con- 
tributes no  plant-food  material.  A  soil  with  a  great  deal 
of  quartz  is  usually  a  light,  easily  worked  soil. 

On  weathering  feldspar  contributes  to  soils  a  mass  of 
very  finely  divided  matter  known  as  clay,  the  smallest  of 
the  soil  particles.     It,  therefore,  forms  part  of  the  clay  in 


Plate  II.  Soil  Formation.  —  Heat,  cold,  and  frost  have  been  largely 
instrumental  in  fracturing  the  rocks  in  the  upper  figure,  and  in  produc- 
ing the  rock  debris  and  soil  in  the  lower.  Note  that  vegetation  has 
already  well  started  on  the  slope. 


SOIL  AS  A   MEDIUM  FOR  PLANT  GROWTH  7 

soils  and  adds  to  their  plasticity,  and  in  addition,  this  very 
fine  material  is  an  absorbent,  holding  the  soluble  plant-food 
materials  of  fertilizers  in  a  form  that  prevents  them  from 
leaching  from  the  soil,  and  yet  gives  them  up  to  plants  rather 
easily. 

As  examples  of  the  second  class  we  again  have  the  feld- 
spars as  they  furnish  lime,  magnesia  and  potash;  calcite, 
which  contains  lime ;  hematite,  which  consists  largely  of 
iron ;  dolomite,  which  contains  both  lime  and  magnesia ; 
apatite,  which  furnishes  phosphoric  acid  and  lime,  and  gyp- 
sum, which  is  a  combination  of  lime  and  sulfur. 

These  minerals  and  the  plant-food  materials  contained 
in  them  may  be  reviewed  in  tabular  form  thus : 


Mineral 

Plant-food  Material 

Feldspars 

Potash,  lime,  magnesia 

Calcite 

Lime 

Dolomite 

Lime,  magnesia 

Hematite 

Iron 

Apatite 

Phosphoric  acid,  lime 

Gypsum 

Sulfur,  lime 

Quartz 

Silica  (not  a  plant-food  material) 

As  these  minerals  are  widely  distributed  in  rocks  from 
which  soils  are  formed,  they  are  found  in  almost  all  soils, 
and  thus  it  is  that  all  the  substances  required  by  plants  are 
to  be  found  in  most  soils. 

QUESTIONS 

1.  What  are  the  properties  of  soil  that  make  it  well  adapted  to 
furnish  a  mechanical  support  for  plants? 

2.  What  relation  does  soil  have  to  the  needs  of  plants  for  water? 

3.  Describe  the  reasons  why  plants  need  water. 

4.  Name  the  elemental  substances  that  plants  derive  from  soil. 

5.  What  elemental  substance  do  plants  obtain  from  soil  that  is 
not  present  in  rocks  from  which  soil  is  formed? 

6.  What  two  substances  necessary  to  plant  growth  are  contained 
in  the  earth's  crust  in  the  smallest  quantities  ? 


8  SOILS  AND  FERTILIZERS 

7.  In  what  way  were  igneous  rocks  formed  ?  Sedimentary 
rocks  ?     Metamorphic  rocks  ?     Name  examples  of  each. 

8.  Name  a  mineral  containing  potash,  a  mineral  containing  lime, 
a  mineral  containing  magnesia,  a  mineral  containing  phosphoric  acid, 
a  mineral  containing  sulfur,  a  mineral  containing  iron. 

LABORATORY   EXERCISES 

The  following  exercises  are  designed  to  suggest  possible  experi- 
ments and  demonstrations  that  may  be  carried  out  in  connection 
with  the  various  chapters.  Some  may  be  performed  by  the  student 
if  adequate  facilities  are  at  hand,  some  are  only  possible  as  demon- 
strations, while  others  are  field  studies  and  depend  on  local  condi- 
tions. Enough  suggestions  are  made  with  each  chapter  to  give  the 
teacher  a  range  of  choice  according  to  his  conditions  and  facilities. 
It  is  not  considered  possible  or  advisable  that  all  the  experiments 
and  demonstrations  listed  be  carried  out. 

Exercise  I.  —  Study  of  soil-forming  minerals.  (The  teacher  will 
find  an  elementary  text  in  mineralogy  of  great  aid  in  this  experi- 
ment.) 

Materials.  —  Small  specimens  of  quartz,  potash-feldspar,  mica, 
calcite,  apatite,  gypsum  and  hematite.  Also  a  piece  of  a  glass,  a 
knife,  dilute  muriatic  acid,  a  hand-lens  and  flame  (gas  or  alcohol). 

Procedure.  —  Study  the  specimens  according  to  the  following 
outline,  with  a  view  to  identifying  the  minerals  unlabeled.  Use 
hand  lens  where  possible 

Hardness.  —  Determine  hardness  by  the  following  scale. 

Hardness  Mineral 

Scratched  by  finger  nail GypsumN>Mica 

Cut  by  knife Calcite  / 

Scratched  with  difficulty  with  knife     .     .  Apatite 

Scratches  glass Feldspar  —  Hematite 

Scratches  glass  very  easily Quartz 

Color.  —  Observe  color  and  luster  of  the  various  specimens  and 
determine  if  it  is  characteristic  and  useful  in  identifying  the  mineral. 

Cleavage  and  fracture.  —  Do  specimens  split  easily  in  certain  direc- 
tions or  do  they  fracture  ?  What  effect  do  these  characters  have 
upon  the  appearance  of  the  mineral  ? 

Form.  —  Do  the  specimens  seem  to  have  any  crystal  form  that 
is  characteristic  and  useful  in  identification  ? 


SOIL  AS  A   MEDIUM  FOR  PLANT  GROWTH  9 

Action  of  acid.  —  What  is  the  result  if  the  specimen  is  treated 
with  a  few  drops  of  acid  ?     Explain. 

Flame.  —  Hold  a  small  fragment  of  each  mineral  in  the  flame. 
Observe  fusibility  and  change  of  color.  Is  the  flame  given  any 
color  which  is  characteristic  ? 

Exercise  II.  —  Study  of  soil-forming  rocks. 

Materials.  —  Small  specimens  of  granite,  basalt,  shale,  slate, 
limestone,  sandstone  and  quartzite. 

Procedure.  —  Study  the  color,  texture,  and  structure  of  each 
sample.  Identify  the  minerals  present  and  from  this  determine 
the  plant-food  materials  carried  by  each  rock.  Be  prepared  to 
identify  unlabeled  samples  in  laboratory  and  field. 

Exercise  III.  —  To  show  that  plants  give  off  water. 

Materials.  —  Plant  growing  in  small  pot,  a  tumbler. 

Procedure.  —  Place  a  tumbler  over  a  small  plant  and  observe 
the  condensation  of  moisture  on  the  sides.  Where  does  this  mois- 
ture come  from  ?  What  was  its  original  source  ?  How  do  plants 
give  off  water?     Explain  uses  of  water  to  the  plant. 

Exercise  IV.  —  Conditions  for  plant  growth. 

Materials.  —  Small  flower  pots,  rich  soil,  oat  seed. 

Procedure.  —  Fill  four  small  flower  pots  with  a  rich  garden  loam. 
Moisten  well  and  plant  with  oat  seeds.  When  seedlings  are  a  week 
old,  thin  to  desired  number  of  plants.  Grow  for  a  few  weeks  under 
optimum  conditions  and  then  subject  them  to  the  following  condi- 
tions : 

Pot  1.  —  Sunshine  and  optimum  water. 

Pot  2.  —  Sunshine  and  minimum  water. 

Pot  3.  —  Cold,  shade,  and  optimum  water. 

Pot  4.  —  Dark  and  optimum  water. 

Observe  results  and  explain.  More  pots  with  other  conditions 
may  be  tried  at  the  pleasure  of  the  teacher.  , 

Exercise  V.  —  Effect  of  the  different  plant  nutrients. 

Materials.  —  One-gallon  flower  pots,  very  poor  sandy  soil,  nitrate 
of  soda,  acid  phosphate,  muriate  of  potash,  barley  seed. 

Procedure.  —  Fill  five  flower  pots  to  within  an  inch  of  their  tops 
with  poor  sandy  soil.  It  is  essential  to  the  success  of  the  experiment 
that  the  soil  be  poor,  and  also  that  it  shall  be  surface  soil  and  con- 


10  SOILS   AND   FERTILIZERS 

tain  some  plant  food  material.     Weigh  the  soil  that  is  placed  in  each 
pot,  mixing  with  it  fertilizer  in  the  following  proportions : 

Pot  1,  nitrate  of  soda  one  part  to  five  thousand  parts  of  soil. 
Pot  2,  acid  phosphate,  one  part  to  five  thousand  parts  of  soil.  Pot 
3,  muriate  of  potash,  one  part  to  ten  thousand  parts  of  soil.  Pot  4, 
all  three  of  these  carriers,  each  at  the  rate  specified  above.  Pot  5, 
no  fertilizer.  Mix  the  fertilizer  and  soil  thoroughly  before  placing 
in  the  pots.  Plant  a  dozen  or  more  barley  seeds  in  each  pot.  Add 
water  in  sufficient  quantity  to  make  the  soil  moist  but  not  too  wet. 
Place  the  pots  in  a  place  that  is  moderately  warm  during  the  day, 
where  they  will  not  freeze  at  night,  and  where  there  is  abundant 
light.  When  seedlings  are  a  week  old,  thin  to  ten.  Allow  plants  to 
grow  for  use  in  laboratory  exercises  in  Chapters  XI,  XII  and  XIII. 
Observe  growth  in  each  pot. 


CHAPTER  II 
SOIL  FORMATION  AND   TRANSPORTATION 

Side  by  side  are  to  be  seen  rock  and  soil.  On  the  rock 
no  vegetation  is  growing  except  a  few  lichens  and  other 
minute  plants.  On  the  soil  there  is  a  luxuriant  growth  of 
multitudinous  plants.  Soil  is  derived  from  rock.  Evi- 
dently there  must  have  been  a  profound  change  to  cause 
such  a  difference  in  their  relations  to  plant  growth.  In 
some  regions  of  the  earth  there  is  much  rock  and  little 
soil,  while  often  on  the  prairie  one  sees  no  large  rocks,  and 
may  plow  all  day  and  perhaps  not  strike  even  a  small 
boulder.  It  may  be  surmised  that  in  connection  with  the 
process  of  soil  formation  there  has  been  a  large  transporta- 
tion of  material  from  one  place  to  another.  All  this  was 
brought  about  by  natural  agencies,  most  of  which  are  still 
operating  to  form  more  soil  and  to  increase  the  productive- 
ness of  soil  already  under  cultivation. 

The  process  of  soil  formation  is,  however,  extremely 
slow,  and  it  must  be  remembered  that  thousands  and  tens 
of  thousands  of  years  have  elapsed  while  the  operation  has 
been  in  progress. 

9.  Agencies  concerned  in  soil  formation  and  transporta- 
tion. —  The  agencies  that  have  brought  about  these  trans- 
formations may  be  listed  as  follows : 

Heat  and  cold  Ice 

Frost  Wind 

Water  Gases 

Plants  and  animals 
11 


12  SOILS  AND   FERTILIZERS 

10.  Action  of  heat  and  cold.  —  Rocks,  as  we  have  seen, 
are  mixtures  of  different  minerals.  These  minerals  have 
different  rates  of  expansion  when  heated.  Exposed  rock  will 
suffer  great  changes  in  temperature  in  twenty-four  hours, 
especially  if  it  be  located  in  a  region  of  high  altitude  and 
cloudless  weather.  A  block  of  marble  one  hundred  feet 
long  will  expand  one-half  inch  with  a  change  of  75°  Fahren- 
heit, and  this  is  frequently  of  diurnal  occurrence  in  an  arid 
climate.  Because  the  minerals  composing  rock  expand  and 
contract  at  different  rates,  they  tend  to  tear  apart,  thus 
producing  crevices  that  may  fill  with  water,  and  this  water 
acts  still  further  to  disintegrate  the  rock. 

11.  Action  of  frost.  —  One  reason  that  building  stones 
are  more  likely  to  disintegrate  in  a  cold  moist  climate  than 
in  a  dry  or  warm  one  is  that  the  small  pores  and  cracks  on 
their  surfaces  fill  with  water,  which,  when  it  freezes,  exerts 
an  enormous  pressure.  The  expansive  power  of  freezing 
water  amounts  to  about  150  tons  to  a  square  foot,  which  is 
equivalent  to  a  column  of  rock  a  third  of  a  mile  in  height. 
The  rock  surface  becomes  chipped  off  by  repeated  freezing 
and  even  great  masses  of  rock  are  detached  by  the  freezing 
of  water  in  larger  cracks,  as  may  be  seen  beneath  rock  ledges 
in  the  spring  of  the  year. 

An  interesting  example  of  the  effect  on  rock  disintegration 
of  a  cold  moist  climate  as  compared  with  a  dry  one  is  found 
in  the  difficulty  that  has  been  experienced  in  preserving 
the  obelisk,  now  in  Central  Park,  New  York,  which  had  pre- 
viously stood  for  many  hundreds  of  years  in  the  Egyptian 
desert  without  great  damage.  It  has  been  found  necessary 
to  cover  the  entire  surface  of  the  stone  with  paraffine  in 
order  to  preserve  the  hieroglyphics  carved  on  its  surface. 

12.  Action  of  water.  —  Water  has  another  effect  on  rock. 
It  is  a  solvent,  weak  but  universal.  It  acts  on  all  minerals,  dis- 
solving slight  quantities  of  some,  considerably  more  of  others. 


Plate  III.  Water  Erosion.  —  The  wearing  action  of  water  is  slow 
but  constant,  and  is  leveling  the  surface  of  the  earth  at  the  rate  of  an 
inch  in  several  hundred  years. 


SOIL  FORMATION  AND   TRANSPORTATION        13 

It  is  as  a  transporting  agent  that  water  is  most  active. 
From  the  time  when  raindrops  beat  down  on  the  surface 
of  the  soil,  while  they  are  gathering  into  rivulets  and  the 
rivulets  are  becoming  rivers  that  discharge  into  the  ocean, 
they  are  engaged  in  moving  particles  of  rock  debris  and 
soil.  It  is  estimated  that  the  United  States  is  being  planed 
down  at  the  rate  of  one  inch  in  seven  hundred  and  sixty 
years.  This  is  rapid  enough  if  it  were  applied  at  one  point 
to  dig  the  Panama  Canal  in  seventy-three  days. 

The  carrying  power  of  water  has  resulted  in  the  formation 
of  the  rich  river  valley  soils  that  have  been  deposited  by 
the  streams  flowing  through  them.  The  coastal  soils  and 
lake  soils  have  also  been  transported  by  water. 

13.  Action  of  ice.  —  In  former  times  a  considerable  part  of 
the  northern  United  States  was  covered  by  huge  masses  of  ice, 
known  as  glaciers.  These  ice  masses  were  of  enormous  vol- 
ume and  moved  slowly  in  a  southerly  direction.  The  great 
thickness  of  the  ice  mantles,  amounting  to  several  thousand 
feet  at  some  places,  caused  them  to  cover  hills,  valleys  and 
mountains,  and  their  enormous  weight  ground  rock  surfaces, 
pushed  forward  heaps  of  soil  and  transported  huge  boulders. 
The  southern  limit  of  the  glaciers  corresponded  roughly  to 
the  lines  now  marked  by  the  Ohio  and  Missouri  rivers,  and 
again  extended  farther  southward  along  the  Pacific  coast. 
It  met  the  Atlantic  coast  at  about  the  present  location  of 
New  York.  Changes  of  climate  caused  an  alternate  reces- 
sion and  extension  of  the  ice  sheets  several  times,  and  during 
all  this  period  soil  was  being  formed  and  worked  over  by 
the  ice  and  the  water  that  melted  from  it.  When  the  glacier 
melted,  stranded  ice  masses  remained  .behind.  These  formed 
lakes  in  which  soil  was  reworked  and  shifted,  and  as  the 
lakes  finally  drained  off,  the  reworked  soil  was  left  behind. 
These  glacial  soils  are,  as  a  rule,  productive,  because  of  the 
thorough  pulverization  and  mixing  they  have  received. 


14  SOILS  AND  FERTILIZERS 

14.  The  action  of  wind.  —  That  wind  has  been  an  active 
factor  in  the  transporation  of  soil  is  evident  to  any  one 
who  has  lived  in  an  arid  or  semi-arid  region,  where  dust 
storms  are  not  infrequent.  In  a  humid  region  the  move- 
ment of  soil  by  wind  is  not  so  patent,  but  even  there,  espe- 
cially along  the  seacoast,  there  is  some  movement  of  this 
kind.  There  is  also  an  erosive  action  produced  by  wind,  but 
this  has  not  been  very  important.  However,  in  arid  regions 
the  sand-bearing  wind  has  been  instrumental  in  wearing 
away  large  surfaces  of  rock,  the  eroded  portions  of  which 
have  helped  to  form  soil. 

The  most  important  result  of  wind  action  has  been  the 
production  of  loessial  soils,  which  are  found  in  parts  of  Wis- 
consin, Illinois,  Iowa,  Missouri,  Nebraska  and  Kansas, 
also  in  the  valley  of  the  Rhine  and  in  parts  of  China.  An- 
other result  is  the  production  of  adobe  soils,  which  are  found 
in  mountain  sections  of  western  and  southwestern  United 
States.  While  these  soils  do  not  owe  their  present  location 
entirely  to  the  action  of  wind,  that  element  has  played  a 
large  part  in  removing  them  from  other  regions  and  depos- 
iting them  where  they  now  are. 

15.  Action  of  gases.  —  Of  the  gases  that  compose  the 
normal  atmosphere,  oxygen  and  carbon  dioxide  are  instru- 
mental in  decomposing  rock  and  soil.  They  unite  chemi- 
cally with  some  of  the  substances  composing  rocks,  and 
when  the  new  compound  thus  formed  is  more  soluble  than 
the  original  substance,  the  resistance  of  the  rock  to  water 
is  decreased.  This  is  a  very  constant  operation,  and  as  air 
penetrates  deeply  into  soil  and  into  the  pores  of  rock  its 
action  is  widespread. 

16.  Action  of  plants  and  animals.  —  Some  of  the  lower 
forms  of  plants,  of  which  lichens  are  a  notable  example, 
are  able  to  live  on  the  bare  surfaces  of  rock,  fastening  them- 
selves to  the  small  crevices  and  pores  and  in  the  process  of 


SOIL  FORMATION  AND   TRANSPORTATION        15 

their  growth  causing  the  rock  to  decay  and  organic  matter 
to  accumulate  in  the  crevices.  These  plants  are  followed  by 
higher  vegetation,  the  roots  of  which  are  larger ;  when  these 
roots  extend  themselves  into  cracks  in  the  rock  they  exert 
a  prying  action  when  wind  gives  the  plant  a  swaying  motion. 

After  rock  becomes  sufficiently  pulverized  to  produce 
soil,  plants  are  active  agents  in  decomposing  soil  particles 
by  the  solvent  action  of  the  acid  secreted  by  their  roots 
and  formed  by  their  decay. 

Very  small  plants,  included  among  the  microorganisms 
because  they  are  too  small  to  be  seen  without  a  microscope, 
are  also  concerned  in  rock  decay.  Their  action  is  exerted 
principally  in.  soil,  and  is  due  to  the  production  of  acids  even 
stronger  than  that  secreted  by  the  roots  of  higher  plants. 

17.  Powdered  rock  is  not  soil.  —  We  have  seen  that  in 
the  process  of  soil  formation  the  rock  is  pulverized,  but  the 
process  of  weathering  to  which  nature  resorts  is  different 
in  its  result  from  merely  grinding  rock  in  a  crusher  or  mortar. 
At  the  same  time  that  the  particles  are  becoming  smaller, 
certain  chemical  changes  are  going  on  that  produce  a  ma- 
terial having  a  different  composition  from  the  original  rock. 
One  result  of  the  transition  is  the  removal  of  a  part  or  some- 
times all  of  the  more  soluble  constituents  of  the  rock.  The 
percentage  loss  of  some  of  the  constituents  of  granite  and 
of  limestone  in  the  process  of  forming  a  clay  is  as  follows : 

Table    1.  —  Percentage   Loss   of   Plant-Food   Materials   in 
Granite  and  Limestone  in  Process  of  Soil  Formation 


Constituents 

Percentage  of  Loss 

Granite 

Limestone 

Phosphoric  acid 

Potash 

Lime 

0.00 

83.52 

100.00 

74.70 

68.78 
57.49 
99.83 

Magnesia 

99.38 

16  SOILS  AND  FERTILIZERS 

This  table  represents  merely  two  cases,  and  is  not  meant 
to  imply  that  these  losses  always  occur  in  just  these  propor- 
tions whenever  rocks  of  this  type  are  converted  into  soil. 
It  will  be  noticed  that  some  of  the  most  valuable  plant-food 
materials  are  lost  in  large  quantities.  For  instance,  practi- 
cally all  the  lime  has  been  lost,  as  has  also  a  large  propor- 
tion of  the  magnesia  and  potash.  Phosphoric  acid  shows 
great  variation  in  respect  to  loss. 

Other  changes  that  occur  in  weathering  include  the  forma- 
tion of  extremely  fine  particles  that  give  plasticity  to  soils, 
and  that  have  the  property  of  absorbing  certain  substances, 
like  fertilizers,  from  solution  and  holding  them  in  a  condition 
in  which  they  do  not  leach  readily  from  the  soil,  and  yet  in 
a  form  in  which  roots  may  make  use  of  them.  As  these 
particles  are  very  small,  we  find  a  relatively  large  propor- 
tion of  them  in  a  clay  soil,  but  a  very  small  proportion  in 
a  sand. 

Another  operation  that  accompanies  soil  formation  is 
the  incorporation  of  vegetable  matter  or  animal  remains  — 
together  called  organic  matter  —  with  the  soil  particles. 
This  adds  greatly  to  the  crop-producing  power  of  a  soil, 
for  as  the  organic  matter  decays  it  makes  more  soluble 
the  inorganic  constituents. 

QUESTIONS 

1.  Name  the  agencies  concerned  in  soil  formation  and  trans- 
portation. 

2.  In  what  way  do  heat  and  cold  act  to  decompose  rock  ? 

3.  What  is  the  action  of  frost  on  rock  ? 

4.  How  does  water  aid  in  the  transportation  of  soil  ? 

5.  What  part  did  the  great  glaciers  play  in  soil  formation  ? 

6.  Has  wind  been  more  potent  as  a  soil  former  or  as  a  trans- 
porter ? 

7.  Describe  the  ways  in  which  roots  aid  in  the  decomposition 
of  rocks. 

8.  Explain  the  difference  between  powdered  rock  and  soil. 


Plate  IV.  Plants  as  Soil  Formers.  —  Plants  are  active  agents  in 
the  decomposition  of  rock.  In  the  upper  figure  lichens  may  be  seen 
beginning  the  disintegration,  and  in  the  lower,  large  tree  roots  are  forcing 
themselves  into  the  cracks  in  the  rock. 


SOIL  FORMATION  AND   TRANSPORTATION        17 

LABORATORY   EXERCISES 

Exercise  I.  —  Soil  formation  and  transportation. 

This  exercise  is  based  on  observations  in  the  field  and  its  value 
depends  on  examples  available.  Use  Chapter  II  as  a  basis  for  the 
field  observations. 

If  rock  outcrops  can  be  found  in  the  neighborhood,  a  visit  to  them 
would  be  worth  while.  Examples  of  wind  action,  heat  and  cold, 
frost,  and  plant  and  animal  influences  in  forming  or  transporting  soil 
should  easily  be  found.  The  erosive  and  carrying  power  of  streams 
should  also  be  studied  in  relation  to  soil  formation. 

An  examination  of  weathered  rock  of  various  kinds  should  be 
made  in  order  to  illustrate  the  chemical  phase  of  soil  formation. 
The  rusting  of  iron  could  be  used  as  an  example  of  the  effect  of 
gases.  The  iron  of  rocks  rusts  in  the  same  way.  This,  together 
with  the  assumption  of  water  and  a  loss  of  soluble  materials,  brings 
about  the  decay  of  the  rock.  Remember,  however,  that  the 
physical  and  chemical  agencies  work  hand  in  hand  and  that  these 
agencies  are  as  active  upon  the  soil  as  upon  the  original  rocks.  An 
examination  in  the  spring  of  fall-plowed  land  would  permit  a  study 
of  the  effect  of  weathering  on  soil  structure. 


CHAPTER  III 
SOIL  FORMATIONS 

From  the  preceding  description  of  the  processes  of  soil 
formation,  it  will  be  seen  that  the  operation  may  involve 
the  transfer  of  soil  from  one  place  to  another,  or  that  it 
may  take  place  in  one  locality,  leaving  the  resulting  soil 
where  the  parent  rocks  stood.  The  latter  soils  are  called 
sedentary,  the  former  transported.  These  may  again  be 
subdivided  as  follows : 

a    ,  f  Residual  —  formed  in  place 

Sedentary     \  ~        ,  .     • 

I  Cumulose  —  plant  remains 

Colluvial  —  gravity  deposits 
Alluvial  —  stream  deposits 
Marine  —  ocean  deposits 
Lacustrine  —  lake  deposits 
Glacial  —  ice  deposits 
.  iEolian  —  wind  deposits 


Transported 


18.  Residual  soils.  —  Soils  of  this  formation  are  geologi- 
cally old,  that  is,  they  were  formed  at  an  earlier  period  than 
any  of  the  other  arable  soils.  They  always  bear  more  or 
less  resemblance  in  composition  to  the  rocks  underlying 
them,  although,  on  account  of  their  great  age  they  have  lost 
much  of  the  more  readily  soluble  constituents  of  the  original 
rock.  This  is  also  of  agricultural  significance,  because 
many  of  these  soluble  constituents  are  of  great  importance 

18 


SOIL  FORMATIONS 


19 


in  the  growth  of  plants.  The  following  table  shows  the 
partial  composition  of  an  Arkansas  limestone  and  of  the 
clay  soil  formed  from  it,  also  the  percentage  of  each  of  the 
constituents  lost  in  the  process : 

Table  2. —  Partial  Composition  op  Limestone  Rock  and  Its 
Residual  Clay 


Constituents 

Percentage  Composition 

Rock 

Soil 

Lost 

Potash 

Lime 

Magnesia 

Iron 

Silica 

0.35 
44.79 
0.30 
2.35 
4.13 

0.96 
3.91 
0.26 
1.99 
33.69 

66.36 
98.93 
89.38 
89.56 
0.00 

It  will  be  seen  from  the  above  table  that  lime,  magnesia 
and  potash  have  disappeared  in  large  quantities,  as  has  also 
iron,  but  that  silica  has  lost  little  or  none  of  what  was  orig- 
inally present,  and  now  constitutes  by  far  the  larger  part 
of  the  soil.  Silica  although  not  of  great  importance  as  a 
plant  nutrient  is,  nevertheless,  of  value  in  crop  production, 
because  it  contributes  to  the  formation  of  the  absorptive 
compounds  before  mentioned. 

The  great  age  of  residual  soils  has  also  led  to  changes  in 
the  composition  of  iron  compounds,  producing  usually  those 
of  a  red  or  yellow  color,  these  colors  being  characteristic  of 
residual  soils.  The  long  period  of  weathering  has  frequently 
resulted  in  wearing  down  the  particles  to  such  a  degree  of  fine- 
ness that  heavy  soils  of  the  nature  of  clay,  clay  loam  or  silt 
are  produced. 

Analyses  of  two  typical  residual  soils  from  Virginia,  that 
have  been  formed  from  gneiss  and  limestone  respectively, 
are  given  in  the  following^table : 


20 


SOILS  AND  FERTILIZERS 


Table  3.  —  Percentage  Composition  op  Typical  Residual 
Soils  from  Virginia 


Constituents 

Original  Rock 

Gneiss 

Limestone 

Phosphoric  acid        

Potash 

Lime 

0.47 

1.10 

trace 

0.40 

12.18 

45.31 

0.10 
4.91 
0.51 

Magnesia         

Iron        

1.20 
7.93 

Silica 

57.57 

A  striking  feature  is  their  low  lime  content,  which  is 
characteristic  of  soils  that  have  been  long  subjected  to 
leaching.  Such  soils  would  require  applications  of  lime  for 
the  profitable  production  of  most  crops.  The  low  content 
of  lime  in  the  soil  derived  from  limestone  illustrates  the 
fact  that  such  an  origin  does  not  insure  a  satisfactory  supply 
of  lime. 

19.  Distribution  of  residual  soils.  —  These  soils  are 
widely  distributed  in  the  United  States,  being  found  in  four 
great  provinces  —  the  Piedmont  plateau  along  the  eastern 
slope  of  the  Appalachian  mountains,  the  Appalachian  moun- 
tains and  plateaus,  the  limestone  valleys  and  uplands  be- 
tween and  west  of  these  mountains,  and  the  Great  Plains 
west  of  the  Mississippi  and  Missouri  rivers. 

20.  Cumulose  soils.  —  Unlike  residual  soils,  cumulose 
soils  are  of  very  recent  origin.  They  have  been  formed  by 
the  growth  of  vegetation  in  and  around  lakes,  ponds  and 
marshes,  many  of  which  were  left  by  the  retreating  glaciers. 
As  the  plants  die  they  become  immersed  in  water,  which 
shuts  off  the  supply  of  air,  and  thereby  arrests  decomposi- 
tion.    The   partly   decomposed   plant  remains  accumulate 


SOIL  FORMATIONS 


21 


until  the  surface  of  the  water  is  reached,  when  larger  plants 
take  root,  and  it  is  not  uncommon  to  find  large  forests 
covering  soil  formed  in  this  way.  Cumulose  soils,  as  may 
be  expected  from  their  mode  of  formation,  contain  a  very 
large  proportion  of  organic  matter.  On  the  basis  of  the 
degree  of  decomposition  of  the  organic  matter  they  have 
been  divided  into  two  classes  —  peat  and  muck.  In  peat 
the  stem  and  leaf  structure  of  the  original  plants  may  still 
be  detected.  In  muck,  however,  decomposition  has  gone 
so  far  that  the  organic  matter  forms  a  more  or  less  homo- 
geneous mass,  and  is  mixed  with  a  larger  proportion  of  min- 
eral matter  than  in  peat. 

Peat  is  used  extensively  as  fuel  in  some  European  coun- 
tries, but  is  not  of  much  value  for  agricultural  purposes. 
The  degree  of  decomposition  reached  by  the  organic  matter 
determines  its  usefulness  for  both  these  purposes.  Muck 
cannot  profitably  be  used  for  fuel,  but  some  muck  lands 
are  highly  prized  for  market-gardening  and  other  of  the 
more  intensive  agricultural  operations. 

The  following  table  shows  the  composition  of  some  typical 
cumulose  soils : 


Table  4. 


Percentage  Composition  of  Some  Cumulose 
Soils 


Constituents 

Percentage  Composition 

Muck 

Muck 

Marsh  Mud 

Mineral  matter 

Organic  matter 

Nitrogen 

Phosphoric  acid 

Potash 

31.60 

68.40 

2.63 

0.20 

0.17 

24.79 

67.63 

2.03 

0.19 

0.15 

80.40 
15.77 

0.15 
0.65 

1  Not  determined. 


22  SOILS   AND   FERTILIZERS 

Many  muck  soils  are  underlaid  by  deposits  containing 
lime  derived  from  shells  of  aquatic  organisms  that  inhabited 
the  bodies  of  water  in  which  the  muck  was  formed.  This 
adds  materially  to  the  value  of  the  land,  as  lime  is  a  valuable 
soil  amendment,  particularly  on  muck  land.  It  is  well  to 
keep  this  in  mind  when  examining  muck  land. 

The  percentage  of  potash  is  much  lower  than  in  any  other 
kind  of  soils,  and  a  potash  fertilizer  is  usually  of  great  benefit 
to  crops  planted  on  muck. 

21.  Colluvial  soils.  —  On  all  steep  slopes  there  is  a  gradual 
downward  creep  of  soil  particles  due  to  the  effect  of  gravity 
assisted  by  rainfall,  freezing  and  thawing,  the  movements 
of  animals,  in  fact  any  agency  that  starts  the  particles  in 
motion,  after  which  their  direction  is  almost  invariably 
downward.  This  soil  formation  is  not  extensive,  nor  in  any 
sense  important.  Such  soils  are  confined  largely  to  the 
bases  of  mountains.     They  are  usually  shallow  and  stony. 

22.  Alluvial,  soils.  —  A  stream  flowing  through  its  valley 
will  erode  its  bed  if  very  steep  and  will  deposit  sediment 
if  nearly  level,  but  under  most  circumstances  it  both  erodes 
and  deposits  soil.  As  the  upper  reaches  of  a  river  are  usually 
of  steeper  grade  than  the  lower,  it  often  happens  that  con- 
siderable material  is  picked  up  by  the  stream  near  its  source, 
and  as  the  current  becomes  slower  farther  down,  this  material 
is  deposited.  Alluvial  soil  is,  therefore,  found  most  largely 
along  rather  slowly  flowing  streams. 

It  is  estimated  that  water  flowing  at  the  rate  of  three 
inches  a  second  will  carry  only  fine  clay,  but  if  this  rate  is 
increased  to  twenty-four  inches  a  second,  pebbles  the  size 
of  an  egg  will  be  moved  along  the  stream  bed. 

It  is  quite  customary  for  streams  flowing  through  a  flat 
region  both  to  erode  and  deposit  soil.  Such  streams  are 
likely  to  be  sinuous  in  their  course,  the  curves  gradually 
becoming  more  angular  as  the  current  erodes  the  soil  from 


SOIL  FORMATIONS  23 

the  concave  bank  and  deposits  it  on  the  convex.  Finally 
the  curve  becomes  so  great  that  the  stream  breaks  through 
the  banks  and  straightens  its  course.  In  this  way  a  broad 
valley  may  gradually  be  covered  by  sediment  deposited  by 
the  stream. 

Changes  in  velocity  of  a  stream,  as  when  in  flood  after 
heavy  rains  or  melting  snows,  cause  a  change  in  its  canying 
power.  Much  material  will  be  picked  up  by  a  stream  in 
flood  that  must  be  deposited  as  the  flood  subsides.  A 
stream  may  build  up  its  bed  so  that  the  surface  of  the 
water  is  higher  than  is  the  land  at  some  distance  on 
either  side.  Such  is  actually  the  case  in  the  lower  Mis- 
sissippi valley. 

23.  Character  and  distribution  of  alluvial  soils.  —  Allu- 
vial soils  may  be  sands,  loams  or  clay,  depending  on  the  veloc- 
ity of  the  stream  and  the  nature  of  the  eroded  material. 
It  is  likely  to  be  the  case  that  the  alluvial  deposits  along  the 
upper  stretches  of  a  stream  will  be  sandy,  and  that  the 
material  deposited  will  become  finer  as  the  stream  proceeds. 
Soils  of  this  formation  have  no  very  distinctive  composition. 
Naturally  this  character  depends  on  the  nature  of  the  ma- 
terial farther  up  the  stream,  and  this,  of  course,  varies  in 
different  parts  of  the  country.  Even  along  any  one  stream 
there  may  be  a  wide  diversity  of  material  picked  up  and 
hence  an  alluvial  soil  is  likely  to  be  a  heterogeneous  one. 
The  content  of  organic  matter  is  usually  high,  as  this 
is  carried  and  deposited  with  the  other  matter.  Alluvial 
soil  is  generally  regarded  as  rich  soil,  but  there  are  many 
exceptions.  When  situated  along  slowly  flowing  streams, 
the  land  is  likely  to  need  drainage. 

Alluvial  soils  are  naturally  confined  to  the  margins  of 
streams,  but  they  are  found  along  small  as  well  as  large 
ones,  and  consequently  the  aggregate  area  of  alluvial  land 
is  large.     The  Mississippi  valley  and  its  branches  contain 


24  SOILS   AND   FERTILIZERS 

the  largest  area  of  alluvial  soil  found  anywhere  in  the  United 
States.  Rivers  flowing  through  the  coastal  plain  are  all 
well  lined  with  alluvial  soil  adjacent  to  their  banks. 

24.  Marine  soils.  —  Soils  of  this  formation  have  been 
made  by  material  carried  by  rivers  and  deposited  in  the 
ocean,  whence  they  afterwards  emerged  by  elevation  of  the 
sea  bottom.  They,  therefore,  resemble  alluvial  soil  that 
has  been  worked  and  reworked  by  sea  water.  They  are 
generally  sandy  soils,  as  the  solvent  action  of  water  and  the 
pulverizing  force  of  waves  has  disposed  of  most  of  the  min- 
erals except  quartz.  They  are  light  not  only  in  texture,  but 
also  in  color.  They  are  nearly  always  deficient  in  organic 
matter.  Their  sandy  nature  fits  them  particularly  well  for 
trucking,  and  it  is  to  that  industry  that  a  large  area  of 
marine  soil  is  devoted. 

25.  Distribution  of  marine  soils.  —  A  fringe  of  land  aver- 
aging many  miles  in  width  along  the  Atlantic  coast  from 
Long  Island  southward  and  including  all  of  Florida  is  com- 
posed of  marine  soil.  This  fringe  then  turns  westward 
and  extends  along  the  Gulf  coast  in  a  wide  band  as  far  west 
as  the  Rio  Grande.  The  alluvial  plain  of  the  Mississippi 
river  cuts  through  the  belt,  but  at  this  point  the  marine 
soil  extends  as  far  north  as  Tennessee.  In  the  aggregate 
the  marine  soils  constitute  a  large  area  of  important 
agricultural  land  producing  cotton,  corn  and  other  farm 
crops,  as  well  as  truck  crops  for  which  they  are  especially 
adapted. 

The  following  is  a  statement  of  the  analysis  of  a  typical 
marine  soil  from  the  coastal  plain  in  Maryland : 

Table   5.  —  Percentage   Composition   of   a  Typical  Marine 

Soil 

Phosphoric  acid      .     .     .     0.05     Magnesia 0.35 

Potash 0.70     Iron 0.91 

Lime     . 0.41     Silica 92.30 


Plate  V. 


Soil  Formation.  —  The   upper  figure  shows  a  glacial  till 
soil,  the  lower  an  alluvial  soil. 


SOIL  FORMATIONS  25 

A  striking  peculiarity  of  this  soil  is  the  high  percentage 
of  silica,  due  to  the  fact  that  quartz  is  highly  resistant 
to  the  constant  working  to  which  the  particles  have  been 
subjected  and  which  has  removed  much  of  the  phosphoric 
acid,  potash,  lime  and  magnesia.  Soils  of  this  particular 
type  contain  little  fertility,  but  respond  well  to  fertilization. 

26.  Lacustrine  soils.  —  These  soils  have  been  formed 
in  the  beds  of  lakes  both  ancient  and  comparatively  modern. 
The  older  ones  were  formed  in  the  glacial  lakes,  and  both 
are  soils  that  have  been  worked  over  by  water.  They 
constitute  good  agricultural  soils  and  are  found  from  New 
England  westward  along  the  Great  Lakes,  and  spread  out 
in  a  wide  area  in  the  Red  River  valley. 

27.  Glacial  soils.  — -  The  tremendous  grinding  to  which 
rocks  have  been  subjected  by  glacial  action  has  resulted  in 
a  large  proportion  of  very  fine  particles,  and  consequently 
these  soils  and  subsoils  are  likely  to  be  rather  heavy.  The 
particles  are  jagged  instead  of  having  the  rounded  appear- 
ance found  in  older  soils  and  soils  that  have  been  worked 
over  by  water  for  longer  periods. 

Owing  to  the  fact  that  this  process  of  soil  formation  has 
employed  mechanical  rather  than  chemical  agencies  the 
soils  resemble  the  parent  rock  very  closely.  Unlike  residual 
soils,  glacial  soils  when  formed  from  limestone  are  generally 
rich  in  lime.  If,  on  the  other  hand,  glacial  soils  are  formed 
from  rocks  poor  in  lime,  they  have  a  small  lime  content. 
The  hill  soils  of  southern  New  York  (Volusia  series)  are 
derived  from  shales  poor  in  lime  and  the  soils  share  this 
quality,  while  certain  glacial  soils  of  the  Mississippi  valley 
(Miami  series)  that  are  formed  from  limestone  and  sandstone 
are  rich  in  lime. 

In  the  following  table  are  shown  analyses  of  residual  and 
glacial  soils  from  Wisconsin,  the  original  rocks  from  which 
they  were  formed  having  been  largely  limestone : 


26 


SOILS   AND   FERTILIZERS 


Table  6.  —  Percentage  Composition  op  Residual  and  Glacial 
Clays  from  Wisconsin 


Constituents 

Residual 

Glacial 

1 

2 

3 

4 

Phosphoric  acid      .... 

0.02 

0.04 

0.05 

0.13 

Potash 

1.61 

1.61 

2.36 

2.60 

Lime 

0.85 

1.22 

15.65 

11.83 

Magnesia 

0.38 

1.92 

7.80 

7.95 

Iron 

5.52 

11.04 

2.83 

2.53 

Silica 

71.13 

49.13 

40.22 

48.81 

It  will  be  seen  that  of  the  substances  important  for  their 
plant-food  value  phosphoric  acid  and  potash  are  somewhat 
more  abundant  in  the  glacial  soils,  that  lime  and  magnesia 
are  very  much  more  abundant,  while  the  less  consequential 
substances  are  present  in  large  quantity  in  the  residual  soil. 
This  is  because  the  residual  soil  has  been  subjected  to  more 
leaching. 

28.  JEolisLTi  soils.  —  Following  the  retreat  of  the  glaciers 
there  ensued  a  period  of  aridity,  especially  in  the  southwest 
section  of  the  territory  now  a  part  of  the  United  States.  Into 
these  regions  there  had  been  washed  a  large  quantity  of 
fine  glacial  till,  and  during  the  dry  period  this  was  blown, 
by  high  westerly  winds,  into  a  large  area  in  the  Mississippi 
and  Missouri  valleys,  where  it  is  now  found.  It  has  been 
given  the  name  of  loess  and  on  account  of  its  wide  area  and 
great  fertility  it  is  an  important  agricultural  soil. 

These  soils  are  frequently  of  great  depth,  their  texture 
is  favorable  to  the  maintenance  of  good  tilth  and  in  prairie 
regions  their  long  period  in  grass,  before  they  were  placed 
under  cultivation,  has  given  them  a  good  supply  of  organic 
matter.  The  following  table  contains  a  statement  of 
analysis  of  soils  from  different  sections  of  the  loessal  area : 


SOIL  FORMATION  27 

Table  7.  —  Percentage  Composition  of  Loess 


Location 

of  Soil, 

Iowa 

Mississippi 

Missouri 

Wyoming 

Phosphoric  acid      .... 

0.23 

0.13 

0.09 

0.11 

Potash 

2.13 

1.08 

1.83 

2.68 

Lime 

1.59 

8.96 

1.69 

5.88 

Magnesia 

1.11 

4.56 

1.12 

1.24 

Iron 

3.53 

2.61 

3.25 

2.52 

Silica 

72.68 

60.69 

74.46 

67.10 

All  of  the  important  plant-food  materials,  particularly 
lime,  are  abundant  in  these  soils.  They  rarely  need  liming, 
and  up  to  the  present  time  commercial  fertilizers  have  been 
used  but  little  on  them. 

Adobe  is  the  name  applied  to  another  seolian  soil  similar 
to  loess  in  its  physical  qualities,  but  differing  somewhat 
in  its  mode  of  formation.  It  is  supposed  to  be  a  mixture 
of  loess  with  debris  from  the  mountain  slopes  and  has  been 
formed  under  arid  conditions.  The  soils  thus  formed  are 
extremely  fertile  when  placed  under  irrigation,  which  is 
usually  necessary  for  their  cultivation,  because  they  are 
found  in  Colorado,  Utah,  southern  California,  Arizona,  New 
Mexico  and  arid  portions  of  Texas.  The  composition  of  two 
typical  soils  is  given  below  : 

Table    8.  —  Percentage    Composition    of    Two    Adobe    Soils 


Constituents 

Phosphoric  acid        .     . 

Potash        

Lime 

Magnesia   .... 

Iron       ...... 

Silica 


0.94 
1.71 

13.91 
2.96 
5.12 

44.64 


28  SOILS   AND   FERTILIZERS 

These  soils  show  a  remarkably  high  content  of  phosphoric 
acid  and  an  abundant  supply  of  the  other  substances  needed 
by  plants. 

Sand  dunes  and  volcanic  dust  are  two  other  forms  of 
seolian  soils  but  nowhere  are  these  soils  of  much  agricultural 
importance. 

QUESTIONS 

1.  How  may  soils  be  divided  with  respect  to  the  localities  in 
which  they  have  been  formed  ? 

2.  What  common  plant-food  materials  have  been  lost  in  great- 
est quantities  by  residual  soils  ?  Why  are  these  soils  likely  to  have 
a  large  proportion  of  clay  ? 

3.  In  what  four  regions  of  the  United  States  are  residual  soils 
found  to  be  predominant  ? 

4.  What  is  the  characteristic  constituent  of  cumulose  soils  ? 
For  what  agricultural  purposes  are  muck  soils  largely  used  ?  In 
what  important  plant  nutrient  are  they  likely  to  be  deficient  ? 

5.  How  is  the  velocity  of  a  stream  likely  to  affect  the  nature 
of  a  soil  with  respect  to  its  proportion  of  sand  and  clay  ?  What 
kinds  of  streams  form  little  alluvial  soil  ? 

6.  Why  are  marine  soils  characteristically  sandy  ?  For  what 
agricultural  industry  are  they  frequently  used  ? 

7.  Are  marine  soils  usually  rich  or  poor  in  plant-food  materials  ? 
Why? 

8.  State  over  what  areas  in  the  United  States  lacustrine  soils 
are  found. 

9.  Why  do  glacial  soils  resemble  chemically  the  rocks  from  which 
they  were  formed  ?  What  is  a  characteristic  difference  between 
residual  soil  and  glacial  soil  when  both  are  formed  from  rocks  rich 
in  plant-food  materials  ? 

10.  Describe  the  mode  of  formation  of  the  two  principal  kinds 
of  seolian  soils  in  the  United  States.  Are  they  characteristically 
rich  or  poor  in  plant-food  materials,  and  in  what  one  particularly  ? 

11.  Using  any  map  of  the  United  States  as  a  base  (preferably  a 
colorless  map  showing  the  state  boundaries  and  river  courses),  draw 
lines  tracing  roughly  the  regions  occupied  by  residual,  alluvial,  marine, 
glacial,  and  seolian  soils.  These  areas  may  then  be  shaded  or  colored 
differently  and  a  soil  map  of  the  United  States  thus  be  made. 


Plate  VI.  Stratification.  —  The  upper  figure  illustrates  stratifica- 
tion of  rock,  the  lower  stratification  of  soil.  This  shale  rock  has  at  one 
time  been  soil.     The  soil  may  sometime  be  rock. 


SOIL  FORMATION 


29 


LABORATORY   EXERCISES 

Exercise  I.  —  Classification  of  soils. 

A  study  of  the  various  kinds  of  soils  must  nec-v, 
essarily  be  made  in  the  field.  No  one  locality 
affords  examples  of  all  the  different  kinds  of  soil 
listed  in  Chapter  III.  In  some  places  only  one  or 
two  classes  may  be  available.  In  any  case  make 
all  possible  use  of  the  materials,  studying  each 
soil  as  to  origin,  parent  rock,  color,  depth,  sub- 
soil, organic  matter,  drainage,  general  fertility 
and  crop  adaptability. 

Exercise  II.  —  Use  of  the  soil  auger  in  taking 
soil  samples. 

Material.  —  Soil    auger    and  jars   or  bags  for 
samples. 

Procedure.  —  Explain  the  construction  of  a  soil 
auger  and  then  proceed  with  the  taking  of  a  sam- 
ple of  the  first  eight  inches  of  soil,  removing  the 
soil  in  two  portions.  Then  clean  out  a  hole 
larger  than  the  auger  worm  to  prevent  contami- 
nation of  later  samples  and  take  the  second  eight 
inches  in  the  way  already  described.  Place  sam- 
ples in  bags  or  jars  for  future  reference  or  exhibi- 
tion. Be  sure  that  the  samples  are  representative  ger  for  taking  soil 
of  the  soils  to  be  studied.  samples.      (A) 

These  samples  may  be  used  later  in  the  tests  handle,  (B)  joint, 
for  organic  matter,  acidity,  water  retention,  and  modified^utTing 
other  demonstrations  according  to  directions  in  the  edge, 
laboratory  exercises  to  be  found  elsewhere  in  the 
book. 


Au- 


CHAPTER   IV 
TEXTURE  AND  STRUCTURE  OF  SOILS 

As  a  result  of  the  grinding  to  which  rock  is  subjected  in 
the  process  of  soil  formation,  there  are  to  be  found  in  soils 
particles  of  all  sizes,  from  gravel  and  coarse  sand  down  to 
particles  so  minute  that  they  cannot  be  seen  with  the  highest 
power  microscope,  to  say  nothing  of  the  unassisted  eye. 
In  all  but  very  sandy  soils,  particles  are  generally  gathered 
into  clusters  or  granules.  Texture  is  a  term  used  in  refer- 
ence to  the  size  of  the  particles  in  a  soil ;  the  term  struc- 
ture refers  to  the  arrangement  of  particles  into  granules. 

29.  Shape  of  particles.  —  There  is  no  universal  shape 
for  soil  particles.  They  vary  from  spherical  to  angular, 
and  are  sometimes  rather  elongated,  but  the  occurrence  of 
anything  like  needle  shape  is  not  common.  Soils  formed 
by  erosion  and  wave  action  are  likely  to  have  rounded 
particles,  as  are  also  soils  formed  from  limestone. 

30.  Space  occupied  by  particles.  —  The  number  of  par- 
ticles in  a  given  volume  of  soil  can  only  be  estimated,  their 
minute  size  precludes  an  actual  enumeration.  It  has  been 
estimated  that  the  number  of  particles  in  a  gram  of  soil 
of  certain  different  kinds  is  as  follows : 

Early  truck 1,955,000,000 

Truck  and  small  fruit   .......  3,955,000,000 

Tobacco 6,786,000,000 

Wheat 10,228,000,000 

Grass  and  wheat 14,735,000,000 

Limestone 19,638,000,000 

30 


TEXTURE  AND  STRUCTURE  OF  SOILS 


31 


If  all  the  particles  were  spheres,  it  is  estimated  that  each 
cubic  foot  of  soil  would  have  a  surface  area  on  its  particles 
amounting  to  from  two  to  three  and  one-half  acres. 

31.  Mechanical  analysis  of  soils.  —  A  separation  of  the 
particles  of  a  soil  into  groups,  each  of  which  comprises 
particles  whose  sizes  fall  within  certain  definite  limits,  is 


-Firm  gravel 

•COARSE  5AHD 
-MEDIUM       - 
-FINE 
VERTHME;'' 

SILT 

CL/T/ 


Fig.  2.  —  Relative  sizes  of  soil  particles  in  the  various  grades  into  which 
a  mechanical  analysis  separates  a. soil.  All  are  enlarged  many  times.  Par- 
ticles of  fine  gravel  may  vary  in  size  from  the  largest  circle  to  the  next  largest ; 
coarse  sand  from  the  second  to  the  third ;  medium  sand  from  the  third 
to  the  fourth,  and  so  on.  The  dot  in  the  center  represents  the  largest  clay 
particles ;  the  smallest  cannot  be  shown  in  a  figure  of  this  magnification. 


called  a  mechanical  analysis  of  the  soil.  The  size  limit 
of  these  groups  is  a  purely  arbitrary  matter,  consequently 
it  is  desirable  that  a  universal  system  shall  be  adopted. 
The  classification  in  general  use  in  this  country  is  one  pro- 
posed by  members  of  the  Bureau  of  Soils  of  the  United  States 
Department  of  Agriculture.  It  provides  for  groups  of  the 
following  sizes : 


32 


SOILS   AND   FERTILIZERS 


Diameters  of  Particles 

Millimeters 

Inches 

Fine  gravel     .     . 
Coarse  sand   .     . 
Medium  sand 
Fine  sand       .     * 
Very  fine  sand    . 

Silt 

Clay      .... 

2-1 

1-0.5 
0.5-0.25 
0.25-0.10 
0.10-0.05 
0.05-0.005 
less  than  0.005 

0.08-0.04 

0.04-0.02 

0.02-0.01 

0.01-0.004 
0.004-0.002 
0.002-0.0002 
less  than  0.0002 

32.  Mechanical  analysis  of  some  typical  soils.  —  When 
soils  are  analyzed  according  to  the  mechanical  separation 
just  described,  there  are  shown  to  be  great  differences 
between  some  of  them,  and  soils  that  are  adapted  to  certain 
crops  are  found  to  have  a  somewhat  characteristic  composi- 
tion. It  must  be  remembered,  however,  that  such  dis- 
tinctions are  always  limited  by  climate.  The  following 
table,  based  on  the  work  of  the  Bureau  of  Soils  and  the 
Minnesota  Experiment  Station,  contains  a  statement  of  the 
mechanical  analyses  of  a  number  of  typical  soils : 


Table  9. 


Mechanical  Analyses  of  Soils  and  Subsoils 
Adapted  to  Certain  Crops 


Coarse 
Sand 

Me- 
dium 
Sand 

Fine 
Sand 

Very 
Fine 
Sand 

Silt 

Clay 

Garden  truck  soil,  Norfolk, 

Virginia 

1.42 

28.27 

38.25 

7.51 

21.04 

7.15 

Garden  truck  soil,  Jamaica, 

Long  Island      .... 

19.06 

24.91 

9.65 

10.08 

17.39 

7.25 

Grass  soil,  Hagerstown,  Md. 

0.08 

0.13 

0.53 

10.94 

23.69 

51.75 

Wheat  and  grass  subsoil, 

Kentucky 

0.00 

0.15 

0.25 

2.34 

39.92 

51.77 

Corn  subsoil,  Nebraska 

0.00 

0.00 

0.10 

25.83 

57.00 

9.49 

Potato  soil,  Minnesota  .     . 

0.00 

59.04 

5.60 

28.40 

4.05 

Wheat  soil,  Minnesota  .     . 

0.00 

0.00 

6.18 

30.60 

57.00 

TEXTURE  AND  STRUCTURE  OF  SOILS 


33 


sSOIL-,     MO.  1 


FINE  COARSE 

6  RAVEL      5AN0 


FINE 
SAND 


VERY  FINE 
SAND 


CLAY 


vSOIL-, 

TSDO 

.  a. 

fftf 

1- 

flW 

o 

70 

s 

60 

fe 

tfO 

UJ 

40 

an 

UJ 

?<0 

ll  1 

W 

Cl 

0 

FINE         COARSE.     MEDIUM 
GBAVEL      SAND        S/4ND 


FINE. 
5AM  D 


VERY  FINE 
SAND         5ILT         CLAY 


Fig.  3.  —  Graphic  statement  of  mechanical  analyses  of  two  soils.  No.  1 
is  a  very  sandy  soil,  and  it  will  be  noted  that  the  bulk  of  its  particles  consist 
of  medium  and  fine  sand.  No.  2  is  a  heavy  clay  and  its  particles  belong 
mainly  to  the  silt  and  clay  divisions. 


33.  Soil  class.  —  The  terms  " sandy  soil,"  "loam  soil," 
"  clay  soil "  and  the  like  have  been  in  such  general  use  and  are 
so  convenient  that  attempts  have  been  made  to  devise  a  sys- 
tematic classification  on  this  basis.     A  soil  class  is  made 


34 


SOILS   AND   FERTILIZERS 


up  of  particles  of  various  sizes,  but  the  proportion  of  the 
large,  medium  or  small  particles  determines  the  class  to 
which  it  belongs.  The  following  table  published  by  Whitney 
will  show  what  percentages  of  soil  separates  are  contained 
in  an  average  sample  of  each  of  the  soil  classes. 


Table  10.  —  Mechanical  Composition 

OF  VA 

rious  Soil  Classes 

Based  on  Averages 

of  Many  Analyses 

Fine 
Gravel 

Coarse 
Sand 

Me- 
dium 
Sand 

Fine 
Sand 

Very 
Fine 
Sand 

Silt 

Clay 

Coarse  sands  .     .     . 

12 

31 

19 

20 

6 

7 

5 

Sands     

2 

15 

23 

37 

11 

7 

5 

Fine  sands      .     .     . 

1 

4 

10 

57 

17 

7 

4 

Sandy  loams  .     .     . 

4 

13 

12 

25 

13 

21 

12 

Fine  sandy  loams     . 

1 

3 

4 

32 

24 

24 

12 

Loam 

2 

5 

5 

15 

17 

40 

16 

Silt  loams  .... 

1 

2 

1 

5 

11 

65 

15 

Sandy  clays    .     .     . 

2 

8 

8 

30 

12 

13 

27 

Clay  loams     .     .     . 

1 

4 

4 

14 

13 

38 

26 

Silty  clay  loams  .     . 

0 

2 

1 

4 

7 

61 

25 

Clays 

1 

3 

2 

8 

8 

36 

42 

There  must  be  a  certain  amount  of  variation  in  the  per- 
centages of  the  separates  that  go  to  make  up  a  soil  class. 
In  order  to  determine  the  class  to  which  a  soil  belongs 
when  its  mechanical  analysis  is  known,  the  diagram  in  Fig. 
4  may  be  used.  If,  for  instance,  a  soil  contains  40  percent 
of  silt  and  15  percent  of  clay,  lines  are  drawn  from  the  point 
marked  40  percent  silt  and  15  percent  clay,  the  lines  being 
parallel  to  the  sides  of  the  right  angle  formed  at  0.  It  will 
be  found  that  these  lines  intersect  in  the  space  marked 
loam,  which  is  the  class  to  which  the  soil  belongs.  If  a  soil 
has  20  percent  silt  and  10  percent  clay,  the  intersection  of  the 
lines  drawn  from  these  points  falls  in  the  space  marked  sandy 
loam,  and  the  soil  belongs  to  that  class.. 


TEXTURE  AND  STRUCTURE  OF  SOILS 


35 


ci^r 


34.  Some  properties  of  the  separates.  —  In  addition  to 
differences  in  their  size,  there  are  other  distinctions  that  are 
more  or  less  characteristic  of  these  separates.  A  mechanical 
analysis,  therefore,  tells  us  something  about  several  of  the 
properties  of  a  soil. 
Clay  particles,  by 
reason  of  their  mi- 
nute size,  tend  to 
make  a  soil  plastic 
and  may  cause  it  to 
become  hard,  com- 
pact and  cloddy 
when  dry.  Silt 
does  this  to  a  much 
less  degree.  The 
extent  to  which  a 
soil  exhibits  these 
properties  depends 
on  its  content  of 
clay  or  silt.  Soils 
containing  much 
clay  or  silt  must  not  be  plowed  when  wet  or  they  will  puddle. 
Both  clay  and  silt  serve  to  increase  the  water-holding  power 
of  a  soil,  and  clay  especially  increases  the  difficulty  of  tillage. 

The  sand  separates  have  the  opposite  properties  of 
clay,  and  in  the  order  of  their  greater  size  of  particles. 
Sandy  soils  are  more  easily  worked,  are  not  likely  to  puddle 
or  to  form  clods,  and  do  not  hold  a  large  amount  of  water, 
but  on  the  contrary  have  a  tendency  to  become  dry.  Sandy 
soils  are  termed  "  light  "  soils  because  they  are  easy  to  till  ; 
clay  soils  are  called  "  heavy  "  because  they  make  a  heavy 
draft  on  the  plow. 

The  absolute  specific  gravity,  or  weight  of  the  particles  as 
compared  with  the  weight  of  the  volume  of  water  which 


Fig.  4.  —  Plan  by  which  the  soil  class  may  be 
ascertained  from  a  mechanical  analysis. 


36 


SOILS   AND   FERTILIZERS 


these  particles  would  displace  if  they  were  immersed  in  it, 
does  not  necessarily  correspond  to  these  terms.  Particles  of 
greater  and  less  specific  gravity  are  scattered  through  both 
"  light "  and  "  heavy  "  soils  and  if  we  are  to  find  the  specific 
gravity  of  a  soil  we  must  have  in  the  sample  to  be  tested 
enough  particles  to  give  an  average  of  all  in  the  soil. 

35.  Chemical  composition  of  soil  separates.  —  The  fact 
that  one  kind  of  mineral  wears  down  to  a  small  particle 
more  easily  than  does  another  indicates  that  there  would  be 
a  preponderance  of  resistant  minerals,  like  quartz,  among 
the  coarse  particles  and  a  large  proportion  of  the  more 
easily  decomposed  minerals,  like  the  feldspars,  among  the 
fine  particles.  This  is  actually  the  case,  and  it  indicates 
a  chemical  difference  in  the  separates.  Analyses  of  sepa- 
rates made  by  the  Bureau  of  Soils  of  the  United  States  De- 
partment of  Agriculture  bring  out  these  differences,  as  shown 
by  the  following  table  : 

Table  11.  —  Chemical  Composition  of  Some  Soil  Separates 


Soils 

Percentage  op 

Phosphoric 

Acid 

Percentage  op 
Potash 

Percentage  op 
Lime 

Sand 

Silt 

Clay 

Sand 

Silt 

Clay 

Sand 

Silt 

Clay 

Crystalline 

residual  . 
Limestone 

residual  . 
Coastal 

plain  .  . 
Glacial  and 

loessial  . 
Arid       .     . 

.07 

.28 

.03 

.15 
.19 

.22 

.23 

.10 

.26 
.24 

.70 

.37 

.34 

.86 
.45 

1.60 

1.46 

.37 

1.72 
3.05 

2.37 

1.83 

1.33 

2.30 
4.15 

2.86 

2.62 

1.62 

3.07 
5.06 

.50 

12.26 

.07 

1.28 
4.09 

.82 

10.96 

.19 

1.30 
9.22 

.94 

9.92 

.55 

2.69 
8.03 

It  will  be  noted  from  this  table  that,  in  general,  the  smaller 
particles  are  richer  in  'phosphoric  acid,  potash  and  lime  than 


TEXTURE   AND  STRUCTURE   OF  SOILS  37 

are  the  larger  ones,  the  only  exception  being  the  lime  in  the 
limestone  residual.  The  arid  soils  do  not  show  as  great 
differences  as  do  the  others,  because  they  have  not  been 
subjected  to  the  same  amount  of  solvent  action  and  tritura- 
tion. 

36.  Soil  structure.  —  By  soil  structure  is  meant  the  ar- 
rangement of  the  particles  of  which  the  soil  consists.  These 
particles  may  be  separated  so  that  each  is  free  to  move 
independently  of  any  other,  which  is  usually  true  of  a  dry 
coarse  sand.  Such  an  arrangement  is  known  as  the  separate 
grain  structure.  On  the  other  hand  the  particles  may  be 
arranged  in  small  groups  or  granules,  these  being  so  firmly 
combined  that  the  granule  acts  like  a  separate  particle. 
The  latter  condition  is  termed  the  granular  or  crumbly 
structure.  When  applied  to  loams  and  clay  soils,  these 
arrangements  of  the  particles  have  a  relation  to  the  condi- 
tion popularly  known  as  tilth.  Good  tilth  in  clays  and  loams 
implies  a  granular  structure,  poor  tilth  a  separate  grain 
structure. 

The  granular  structure  is  not  to  be  confused  with  a  cloddy 
condition  of  the  soil.  In  fact  clods  have  the  separate  grain 
structure,  because  the  soil  has  been  worked  when  wet  until 
the  granules  are  broken  down  and  the  particles  move  easily 
over  each  other  owing  to  the  lubrication  of  the  moisture. 

37.  Relation  of  structure  to  pore  space.  —  The  arrange- 
ment of  the  soil  particles  determines  to  a  considerable  degree 
the  amount  of  free  or  pore  space  within  the  soil,  especially  in 
loams  and  clays.  Merely  for  the  purpose  of  illustrating  this 
let  us  suppose  that  the  soil  particles  are  perfect  spheres  of 
equal  size,  which,  of  course,  they  are  not.  There  would  be  two 
arrangements  possible,  if  each  sphere  were  independent  of 
every  other:  (1)  in  columnar  order,  in  which  each  particle 
is  touched  on  four  places  by  its  neighbors ;  (2)  oblique 
order,  in  which  each  particle  is  in  contact  with  six  of  its 


38 


SOILS   AND   FERTILIZERS 


neighbors.  The  calculated  pore  space  in  the  first  arrange- 
ment is  47.64  percent.  That  in  the  second  case  is  25.95 
percent.     (See  Fig.  5.) 

It  is  not  actually  the  case,  however,  that  soil  particles 
are  of  the  same  size  in  any  natural  soil.  Consequently 
small  particles  fit  in  between  large  ones,  thus  decreasing 
greatly  the  actual  pore  space.  These  three  cases,  of  which 
only  the  last  may  occur  in  nature,  illustrate  pore  space 


Fig.  5.  —  If  all  soil  particles  were  spheres  they  could  be  arranged  as 
shown  above,  in  which  case  the  pore  space  would  vary  in  volume  as  ex- 
plained in  the  text. 

when  the  separate  grain  structure  obtains,  as  in  a  dry  sand 
or  a  puddled  loam  or  clay. 

The  granular  structure  is  the  one  most  likely  to  be  found 
in  nature,  although  all  of  the  particles  may  not  be  in  gran- 
ules. The  granules  being  of  irregular  form,  with  many 
angles,  there  is  likely  to  be  a  large  amount  of  space  between 
them.  It  would  be  possible  under  this  arrangement  for  a 
soil  to  have  a  pore  space  of  72  percent. 

The  weight  of  a  given  volume  of  soil,  including  the  pore 
space,  as  compared  with  an  equal  volume  of  water  is  termed 
the  apparent  specific  gravity.  This  it  will  be  seen  is  not  the 
same  as  the  absolute  specific  gravity  because  the  amount  of 
pore  space  is  the  important  factor  in  determining  the  ap- 
parent specific  gravity.  Neither  do  the  terms  "  light  "  soil 
and  "  heavy  "  soil  bear  any  definite  relation  to  the  apparent 
specific    gravity.    A    knowledge  of    the    apparent  specific 


TEXTURE   AND  STRUCTURE   OF  SOILS 


39 


gravity  of  a  soil  is  useful  because  it  is  an  indication  of  the 
amount  of  pore  space. 

38.  Relation  of  structure  to  tilth.  —  The  term  " tilth"  is 
commonly  used  to  denote  the  condition  of  a  soil  with  refer- 
ence to  plant  growth.  When  the  physical  condition  of  a 
soil  is  favorable  to  plant  growth,  the  soil  is  said  to  be  in 
good  tilth ;  when  the  physical  condition  is  unfavorable,  it  is 
said  to  be  in  poor  tilth.  A  loam  or  clay  soil  to  be  in  good  tilth 
must  have  the  greater  number  of  its  particles  in  a  granular 
condition.  The  more  sandy  a  soil  the  less  the  necessity  for 
a  highly  granular  structure  in  order  that  it  shall  be  in  good 
tilth.  The  greater  the  proportion  of  clay  in  a  soil,  the  more 
necessary  is  the  granular  structure.  One  of  the  great  ob- 
jects in  soil  management  is  to  produce  and  maintain  the 
granular  structure. 

39.  Conditions  and  operations  that  affect  structure.  — 
So  far  as  the  structure  of  a  soil  is  concerned,  something  de- 
pends on  the  inherent  quali- 
ties of  the  soil  and  something 
on  its  treatment  by  the  weather 
and  by  man.  These  factors 
may  be  enumerated  as  follows  : 
(1)  texture,.  (2)  wetting  and 
drying,  (3)  freezing  and  thaw- 
ing, (4)  addition  of  organic 
matter,  (5)  tillage,  (6)  roots 
and  animals,  (7)  lime. 

40.  Relation  of  texture  to 
structure.  —  A  coarse  sand 
admits  only  of  the  separate 
grain  structure.  There  is  not  sufficient  cohesion  to  hold 
the  particles  in  granules,  and  there  is  no  plasticity.  With  a 
decrease  in  the  size  of  the  partieles,  there  is  a  greater  tend- 
ency to  the  formation  of  the  granular  structure,  other  con- 


Fig.  6.  —  Structure  of  a  loam  soil 
in  good  tilth.  (A)  sand  particle, 
(B)  pore  space,  (C)  granule  com- 
posed of  silt  and  clay  particles. 


40  SOILS   AND   FERTILIZERS 

ditions  being  equal.  This  does  not  mean  that  a  clay  soil  is 
easier  to  keep  in  good  tilth  than  is  a  loam  soil,  but  under 
favorable  conditions  the  small  particles  have  greater  plastic- 
ity and  cohesion  and  hence  form  granules  more  readily. 

41.  Wetting  and  drying.  —  As  a  soil  becomes  dry  there 
is  a  contraction  of  volume  in  which  process  lines  of  cleavage 
or  cracks  occur  and  clods  are  formed.  If  these  clods  be 
again  wetted  and  partly  dried  without  working,  they  will 
separate  into  smaller  clods  and  finally  a  granular  structure 
will  be  produced.  This  is  illustrated  by  the  greater  ease 
with  which  clods  may  be  worked  down  after  a  rain  and 
partial  drying,  than  when  they  remain  perfectly  dry.  Land 
in  need  of  drainage  is  usually  in  poor  tilth,  while  after  drain- 
age this  condition  gradually  improves. 

42.  Freezing  and  thawing.  —  The  "  heaving  "  of  roots 
during  winter  is  an  indication  that  frost  has  a  disrupting 
action  on  the  solidarity  of  the  soil.  Roots  are  pried  out 
because  the  surface  of  the  soil  rises  when  freezing  occurs 
and  sinks  when  melting  takes  place.  Water  that  is  held 
between  soil  particles  freezes  when  the  temperature  of  the 
surrounding  soil  falls  below  the  freezing  point.  As  water 
freezes  it  expands,  the  effect  of  which  is  to  force  the  particles 
farther  apart.  The  pressure  applied  by  the  freezing  water 
is  very  unevenly  distributed.  Around  the  larger  water- 
holding  spaces  the  particles  are  moved  farther  than  are 
those  adjacent  to  smaller  spaces,  because  the  larger  the 
body  of  water  the  greater  the  expansion  when  it  freezes. 
The  uneven  crowding  of  the  particles  causes  a  breaking  up 
of  the  soil  into  more  or  less  separate  masses  and  as  this  pro- 
ceeds with  repeated  freezing  and  thawing  there  is  a  pro- 
nounced formation  of  granules  in  a  clay  or  loam  soil. 

Fall-plowed  land,  if  left  unharrowed,  or  if  too  cloddy  to 
work  down  to  a  good  tilth,  will  generally  be  mellow  by  spring, 
provided  there  is  much  freezing  weather  during  the  winter. 


TEXTURE   AND   STRUCTURE  OF  SOILS  41 

43.  Effect  of  organic  matter  on  structure.  —  The  quantity 
of  organic  matter  in  a  soil  is  frequently  the  deciding  factor 
in  determining  its  structure.  Partially  decomposed  organic 
matter  has  a  loose,  spongy  structure  and  at  the  same  time 
a  plastic  quality.  The  latter  causes  the  soil  particles  to 
cohere,  and  the  former  gives  to  the  organic  matter  the 
property  of  swelling  when  the  soil  becomes  wet  and  shrink- 
ing when  it  becomes  dry.  These  changes  in  volume  facilitate 
the  formation  of  granules  as  previously  explained. 

Large  areas  of  land  in  this  country  have  deteriorated  in 
productivity  and  have  become  compact  and  difficult  to  work 
on  account  of  the  gradual  loss  of  organic  matter.  Naturally 
clay  and  heavy  loam  soils  have  suffered  more  in  this  way 
than  have  lighter  soils.  Where  marked  decrease  in  crop 
returns  has  occurred  during  the  time  that  soils  have  been 
under  cultivation,  the  difficulty  can  generally  be  traced  to 
loss  of  organic  matter  more  than  to  any  other  factor  in  plant 
growth.  Compact  soil,  with  consequent  poor  tilth,  is  one 
of  the  most  common  conditions  in  poor  farming  regions, 
and  is  usually  associated  with  a  low  content  of  organic 
matter. 

44.  Roots  and  animals.  —  In  some  way  not  very  well 
understood  roots  exert  more  or  less  influence  on  soil  struc- 
ture. Shallow,  fibrous-rooted  plants,  among  which  are 
the  grasses,  wheat,  barley,  millet  and  buckwheat,  have  the 
most  favorable  action  in  granulating  soil.  More  deeply 
rooted,  and  especially  tap-rooted  plants,  have  this  property 
to  a  less  extent.  In  fact,  a  crop  of  beets  may  help  to  com- 
pact a  soil  already  in  bad  condition.  In  establishing  a  rotation 
it  is  desirable  that  some  fibrous-rooted  plants  form  one  or 
more  of  the  courses. 

Various  forms  of  animal  life  help  to  granulate  soils.  Of 
these,  earthworms  are  the  most  notable.  The  soil  particles 
that  they  excrete  from  the  digestive  tract  may  amount  to 


42  SOILS  AND   FERTILIZERS 

several  tons  in  an  acre  in  the  course  of  a  year,  while  their  bur- 
rows ramify  through  the  soil  in  all  directions.  The  move- 
ment of  soil  particles  that  results  is  an  appreciable  factor 
in  changing  soil  structure.  Insects  and  other  burrowing 
creatures  affect  soil  structure  in  a  similar  way. 

45.  Tillage  and  structure.  —  The  ordinary  operations  of 
tillage  are  designed  to  improve  soil  structure,  and  are  effective 
if  these  operations  are  conducted  at  the  proper  time  and  in 
the  best  way.  Plowing,  which  is  the  most  fundamental  of  all 
tillage  operations,  may  improve  soil  structure  or  may  injure 
it,  depending  on  the  condition  of  the  soil  at  the  time  of 
plowing.  It  is  a  matter  of  common  knowledge  that  working 
a  soil  saturated  with  water  will  cause  it  to  puddle,  or  in 
other  words,  to  assume  the  separate  grain  structure.  Plowing 
when  the  soil  is  very  dry  may  have  the  same  effect,  although 
not  usually  to  the  same  extent.  However,  when  a  soil  is  mod- 
erately moist,  plowing  aids  greatly  in  effecting  a  granular 
structure.  This  it  does  by  the  peculiar  twisting  action  that 
the  curved  moldboard  gives  to  the  furrow  slice.  The  soil 
in  immediate  contact  with  the  plow  surface  is  retarded  by 
friction,  and  the  layers  above  tend  to  slide  over  one  another 
much  as  do  the  leaves  of  a  book  when  they  are  bent.  The 
soil  is  thus  broken  up  into  masses  of  aggregates  correspond- 
ing to  the  location  of  the  lines  of  weakness.  If  a  soil  has 
been  strongly  compacted,  so  that  there  are  few  lines  of  weak- 
ness, the  clods  will  be  large  when  the  soil  is  plowed.  Plow- 
ing helps  to  improve  the  tilth  of  the  soil,  but  it  will  not  over- 
come entirely  a  bad  physical  condition. 

46.  Structure  as  affected  by  lime.  —  One  of  the  properties 
possessed  by  lime  is  that  of  flocculating  clay.  This  may  be 
readily  observed  by  stirring  a  spoonful  of  clay  in  a  tumbler 
of  water  and  then  adding  a  quarter  of  a  spoonful  of  burnt 
lime.  It  will  be  noticed  that  the  soil  settles  much  more 
quickly  after  the  lime  has  been  added  than  before.     Sandy 


Plate  VII.     Tillage.  —  Good  tilth  is  a  response  to  good  soil  manage- 
ment.    The  upper  figure  is  an  illustration  of  poor,  the  lower  of  good,  tilth. 


TEXTURE   AND   STRUCTURE   OF   SOILS  43 

soils  are  not  flocculated  to  the  same  extent  by  lime,  but  are  thus 
affected  in  proportion  to  the  quantity  of  clay  they  possess. 

Of  the  different  forms  of  lime,  quick-lime  and  water- 
slacked  lime  are  more  active  in  producing  a  granulated  struc- 
ture of  soil  than  is  ground  limestone,  marl  or  air-slacked 
lime.  This  is  one  reason  why  the  burned  lime  is  superior 
to  ground  limestone  for  use  on  heavy  clay  soils,  on  which 
there  may  be  a  pronounced  difference  in  the  effect  of  the  two 
kinds  of  lime  on  crop  production.  Warington  reports  a 
statement  of  an  English  farmer  to  the  effect  that  by  the 
use  of  large  quantities  of  lime  on  heavy  clay  soil  he  was 
enabled  to  plow  with  two  horses,  while  three  were  necessary 
before  applying  lime. 

47.  The  soil  survey.  —  The  purpose  of  a  soil  survey  is  to 
classify  and  map  the  soils  in  a  given  area  according  to  their 
crop  relations  and  their  physical  properties,  and  to  correlate 
these  soils  with  those  in  other  areas.  The  soil  unit,  or  what 
may  be  termed  the  soil  individual,  is  the  type,  and  on  a  soil 
map  each  type  is  given  a  different  color.  Every  soil  type 
has  a  certain  peculiar  and  characteristic  appearance  and 
certain  inherent  properties  that  distinguish  it  from  every 
other  type.  When  the  type  is  known  some  practical  infor- 
mation regarding  its  texture  and  its  amenability  to  tillage 
and  to  drainage  may  be  predicted,  and  something  in  regard 
to  its  productiveness  and  the  crops  to  which  it  is  adapted 
may  also  often  be  inferred. 

48.  Classification  of  soils.  —  In  order  to  distinguish 
between  soils,  and  to  give  a  basis  on  which  to  separate  them 
into  the  types  to  which  reference  has  been  made,  a  form  of 
classification  has  been  adopted  in  this  country  that  takes 
into  consideration  much  of  what  is  known  of  their  history 
and  their  properties.  Thus  the  first  large  division  into 
which  a  soil  falls  is  known  as  the  soil  province,  which  is 
based,  in  a  general  way,  on  the  process  of  formation.     A 


44  SOILS   AND   FERTILIZERS 

province  may  represent  residual  soil,  like  the  Piedmont 
province,  or  glacial  soil,  or  marine  soil,  or  soils  of  other 
processes  of  formation. 

The  next  smaller  division  is  the  series.  A  soil  series  has 
been  defined  as"a  group  of  soils  having  the  same  range  in 
color,  the  same  character  of  subsoil,  particularly  as  regards 
color  and  structure,  broadly  the  same  tj^pe  of  relief  (topog- 
raphy) and  drainage,  and  a  common  or  similar  origin." 
The  last  of  these  properties  is  due  to  the  fact  that  soils  of 
the  same  series  must  fall  within  the  same  province. 

The  final  division  is  the  class,  which  has  been  described 
in  paragraph  33.  A  soil  class  is  not  limited  in  its  occurrence 
to  a  soil  province,  but  the  same  class  may  be  found  in  all 
provinces.  In  this  respect  it  differs  from  a  series,  any  one 
of  which  occurs  only  in  a  single  province. 

A  soil  type  represents  a  soil  of  a  single  province,  a  single 
series  and  a  single  class,  and  represents  the  features  of  each. 
The  following  is  an  example : 

Province Piedmont 

Series       .     .     . Cecil 

Class       Clay 

Type       Cecil  clay 

49.  Information  furnished  by  a  soil  survey.  —  The  method 
of  arriving  at  the  identification  of  a  soil  type  involves  a 
history  of  the  soil,  and  that  may  tell  something  about  its 
probable  chemical  composition,  as  may  be  judged  from  the 
tables  of  analyses  of  soils  of  different  formations  (§§  18-28). 
The  series  we  have  already  found  to  signify  something  in 
regard  to  the  working  qualities  of  the  soil,  as  does  also  the 
class.  These  distinguishing  features  are  much  more  marked 
in  some  types  than  in  others ;  in  the  case  of  certain  types 
considerable  definite  information  is  available  when  the  soil 
type  is  known,  while  in  the  case  of  others  less  knowledge  is 
afforded.     Some  types  always  represent  a  defective  soil  due 


TEXTURE   AND  STRUCTURE   OF  SOILS  45 

perhaps  to  lack  of  lime,  or  poor  drainage,  or  they  may 
be  characteristically  deficient  in  phosphoric  acid  or  even 
in  potash.  Again  a  type  is  often  indicative  of  the  kind 
of  crops  to  which  a  soil  is  adapted,  but  as  climate  is  a 
large  factor  in  determining  the  success  of  any  crop,  conclu- 
sions of  this  nature  are  not  of  universal  application.  The 
working  qualities  of  a  soil  may  usually  be  gauged  with 
some  degree  of  certainty  when  the  type  is  known.  It  is, 
however,  as  a  foundation  for  a  further  study  of  soils  that 
the  survey  is  probably  of  greatest  usefulness. 

QUESTIONS 

1.  To  what  does  the  term  "  texture  "  refer  when  used  with  refer- 
ence to  soils  ? 

2.  Name  the  groups  into  which  soils  are  divided  by  a  mechanical 
analysis. 

3.  What  characterizes  the  difference  in  mechanical  composition 
of  soils  adapted  respectively  to  wheat,  corn  and  potatoes  ? 

4.  What  is  meant  by  class  as  applied  to  soils  ? 

5.  In  what  class  does  soil  belong  that  contains  20  percent  clay 
and  20  percent  silt  ?  One  that  contains  40  percent  clay  and  30  per- 
cent silt  ?     One  that  contains  25  percent  clay  and  35  percent  silt  ? 

6.  How  do  soils  containing  a  high  percentage  of  clay  or  silt  be- 
have when  wet  ?  How  is  their  water  capacity  likely  to  compare 
with  that  of  a  soil  high  in  sand  ? 

7.  How  do  coarse  and  fine  particles  usually  differ  with  respect 
to  their  content  of  phosphoric  acid,  potash  and  lime  ? 

8.  What  is  meant  by  soil  structure  ? 

9.  Distinguish  between  separate  grain  structure  and  granular 
structure.     Which  permits  of  the  greater  amount  of  pore  space  ? 

10.  Describe  the  relation  of  tilth  to  structure. 

11.  Explain  relation  of  structure  to  texture. 

12.  Explain  relation  of  structure  to  wetting  and  drying  of  soil. 

13.  Explain  relation  of  structure  to  freezing  and  thawing  of  soil. 

14.  Explain  relation  of  structure  to  organic  matter. 

15.  Explain  relation  of  structure  to  roots  and  animals. 

16.  How  is  structure  affected  by  lime  ? 

17.  How  is  structure  affected  by  tillage  ? 


46  SOILS   AND   FERTILIZERS 

LABORATORY   EXERCISES 

Exercise  I.  —  Examination  of  soil  particles. 

Materials.  —  Samples  of  soil,  hand  lens,  high  power  microscope. 

Procedure.  —  Examine  various  sizes  of  soil  particles  under  the 
hand  lens  and  later  under  the  microscope.  Observe  shape  and 
color.  If  possible  measure  size  of  particles.  Try  to  distinguish 
between  silt,  clay  and  sand  particles. 

Exercise  II.  —  Examination  of  soil  separates. 

Materials.  —  The  seven  separates  into  which  a  soil  is  divided  in 
making  a  mechanical  analysis. 

Procedure.  —  As  a  soil  is  made  up  of  the  seven  grades  of  parti- 
cles in  varying  amounts,  the  characteristics  of  the  grades  will 
determine  the  characteristics  of  the  soil. 

Observe  the  cohesion  and  plasticity  of  each  grade.  The  finer 
grades  are  usually  richer  in  plant  food.  Therefore  try  to  imagine 
the  physical  and  chemical  properties  of  different  mixtures.  Study 
the  separates  with  a  view  to  identification  if  presented  unlabeled. 

Exercise  III.  —  Simple  mechanical  analysis. 

Materials.  —  Sandy  loam  well  pulverized,  8  oz.  bottle,  funnel 
with  filter  paper,  torsion  balance,  ammonia.     (See  Fig.  7.) 

Procedure.  —  Place  50  grams  of  a  dry  and  well-pulverized  sandy 
loam  in  a  bottle  of  about  8  ounces  capacity.  Add  a  few  drops  of 
ammonia  and  fill  two-thirds  full  of  water.  Shake  five  minutes  to 
break  up  all  granules.  Then  allow  sample  to  stand  until  the 
various  grades  of  sand  have  settled  to  the  bottom,  after  which  de- 
cant the  silt  and  clay.  Add  water  and  repeat  this  until  the  water 
clears  as  soon  as  the  sands  have  settled.  Then  wash  the  sands 
out  into  a  weighed  filter  paper  held  in  a  funnel.  Allow  sands  to 
drain.  Then  dry  sands  and  filter  paper  thoroughly  and  weigh. 
This  weight,  less  the  weight  of  the  filter,  will  give  the  weight  of  the 
sands.  Fifty  grams,  less  the  weight  of  the  sands,  will  give  the 
weight  of  the  silt  and  clay.  Calculate  the  percentages  of  sand  and 
of  silt  and  clay  respectively  in  the  sample  of  sandy  loam. 

Exercise  IV.  —  Study  of  soil  class  and  its  determination  by 
examination. 

Materials.  —  Hand  lens,  a  number  of  different  soil  classes  (sand, 
sandy  loam,  clay  loam,  loam,  silt  loam,  muck,  etc.)  labeled  for  study 
and  a  set  of  unknown  specimens  for  identification. 


TEXTURE   AND   STRUCTURE   OF   SOILS 


47 


Procedure.  —  Examine  the  texture  of  each  of  the  labeled  soils 
both  under  the  hand  lens  and  by  the  feel.  Observe  the  color  and 
estimate  the  amounts  of  organic  matter  by  the  darkness  of  the  color. 
Be  able  to  identify  samples  if  unlabeled. 

Observe  the  plasticity  and  cohesion  of  each  soil  when  enough 
water  has  been  added  to  develop  maximum  plasticity.  Make  small 
marbles  of  sand,  clay  and  muck  respectively  when  each  is  at  its 
maximum  plasticity.  Dry  and  observe  relative  cohesion  and 
plasticity.    Be  able  to  state  the  relation  of  texture,  moisture  and  or- 


9       CLAY 


SAND5 


APPARATU5    FOR  FILTERING    5AND3 

Fig.  7   —  Apparatus  for  a  simple  mechanical  analysis  of  soil.     Shaker 
bottle,  funnel,  filter,  beaker  and  stand. 


ganic  matter  to  cohesion  and  plasticity.  What  is  the  practical  im- 
portance of  texture  and  class  ? 

Obtain  set  of  unlabeled  samples  for  identification  of  class.  If 
possible,  pupils  should  also  identify  samples  in  the  field.  As  mois- 
ture variations  and  tillage  operations  often  make  great  differences 
in  the  general  appearance  of  a  soil,  skill  in  quickly  and  accurately 
determining  the  class  of  any  soil  in  the  field  is  a  valuable  asset  in 
all  agricultural  work. 

Exercise  V.  —  Determination  of  soil  class  from  a  mechanical 
analysis. 

Materials.  - —  Figure  on  page  35. 


48 


SOILS   AND   FERTILIZERS 


Procedure.  —  By  the  use  of  the  chart  determine  the  class  of  the 
following  soils  and  describe  their  probable  characteristics. 


Soil 

Fine 
Gravel 

Coarse 
Sand 

Medium 
Sand 

Fine 

Sand 

Very 
Fine 
Sand 

Silt 

Clay 

1 

1 

5 

6 

5 

3 

70 

10    %^ 

2 

2 

3 

10 

18 

12 

45 

10  X- 

3 

1 

2 

14 

18 

25 

30 

10S~i 

4 

2 

3 

25 

14 

16 

30 

10 

5 

3 

7 

25 

30 

20 

10 

5 

6 

2 

3 

12 

19 

24 

10 

30 

7 

1 

4 

9 

11 

10 

40 

25 

8 

2 

2 

3 

4 

4 

60 

25 

9 

1 

2 

7 

6 

4 

20 

60 

10 

2 

1 

3 

2 

2 

50 

40 

u 


fr* 


Be  ready  to  explain  the  practical  value  of  a  mechanical  analysis. 

Exercise  VI.  —  Soil  structure. 

Materials.  —  Puddled  and  granular  soils. 

Procedure.  —  Examine  under  hand  lens  a  granular  and  a  puddled 
soil.  Describe  each  and  make  drawings.  Discuss  each  as  to  prob- 
able relation  to  air  and  water  movement,  penetration  of  plant  roots, 
ease  of  making  seed  bed,  etc.  Be  ready  to  suggest  practicable  reme- 
dies for  poor  structure. 

Exercise  VII.  —  Determination  of  apparent  specific  gravity  of 
a  dry  sand  and  clay.     (See  Fig.  8.) 

Materials.  —  Torsion  balance,  dry  soils  and  a  100  c.c.  graduated 
cylinder. 

Procedure.  —  Apparent  specific  gravity  is  the  weight  of  dry  soil 
compared  to  the  weight  of  the  same  volume  of  water. 

Weigh  the  100  c.c.  graduate  in  grams,  then  fill  to  the  100  c.c. 
mark  with  loose  sand.  Weigh  and  calculate  the  weight  of  the  sand 
in  grams.  The  weight  of  the  sand  divided  by  100  (the  weight  of 
100  c.c.  of  water  in  grams)  will  give  the  apparent  specific  gravity  of 
the  loose  sand.  Now  compact  the  sand  as  much  as  possible  by 
jarring  and  read  volume.  Divide  the  weight  of  the  sand  by  this 
volume  to  obtain  the  apparent  specific  gravity  of  the  sand  compact. 


TEXTURE   AND   STRUCTURE   OF  SOILS 


49 


Determine  in  the  same  way  the  apparent  specific  gravity  of  the 
clay  when  loose  and  when  compact. 

Compare  the  figures  from  each  soil  and  explain  the  reasons  for 
the  differences  observed. 

Calculate  the  weight  per  cubic  foot  and  acre  foot  of  the  sand  and 
clay  when  loose  and  when  compact. 


Fig.  8.  —  Equipment  for  the  determination  of  the  apparent  specific 
gravity  of  soil,  consisting  of  a  balance,  a  set  of  weights  and  a  100  c.c.  gradu- 
ated cylinder. 

Exercise  VIII.  —  Calculation  of  pore  space. 

Materials.  —  Data  from  Exercise  VII. 

Procedure.  —  Using  2.7  as  the  absolute  specific  gravity  of  soils 
and  the  data  from  the  preceding  exercise,  calculate  the  pore  space 
on  loose  and  compact  clay  and  sand  respectively  by  means  of  the 
following  formula. 

%  pore  space  =  100  -  ["ap-sp-gr.  x  l^Ql  ■ 
Labs.  sp.  gr.       1  J 

Be  ready  to  explain  the  reasons  and  significance  of  the  results 
obtained. 

1  Ap.  sp.  gr.  means  apparent  specific  gravity.    Abs.  sp.  gr.  means  absolute 
specific  gravity. 
E 


50 


SOILS   AND   FERTILIZERS 


Exercise  IX.  —  A  study  of  the  plow. 

Material.  —  Garden  plow  and  team. 

Procedure.  —  Study  the  plow  by  following  the  diagram  in  Fig.  9. 
Locate  the  mold  board,  point,  share,  landside,  shin,  heel  beam, 
coulter  and  clevis. 

Adjust  the  plow  to  various  widths  and  depths  of  furrow  slice, 
trying  out  each  adjustment  by  throwing  several  furrows.  Be  sure 
that  with  each  adjustment  the  plow  operates  properly. 


h—?^L^ 


Fig.  9.  —  A  walking  plow  and  its  attachments,  (a)  clevis,  (6)  beam  clevis, 
(c)  bridle,  (d)  beam,  (e)  mold  board,  (/)  depth  wheel,  (g)  rolling  coulter, 
(h)  jointer,  (i)  standard,   (j)  share  point,  shin  above,  (k)  landside. 


Study  the  inversion  of  the  furrow  slice  and  be  ready  to  explain 
how  and  why  a  plow  is  a  good  pulverizing  agent.  The  pupils  should 
hold  the  plow  as  much  as  possible  in  the  various  tests. 

If  a  sod  plow  is  available,  a  study  of  this  form  would  be  of  value, 
comparing  it  with  the  garden  plow  above.  A  comparison  of  a  walk- 
ing plow  with  a  sulky  plow  would  also  be  worth  while. 

A  visit  to  an  implement  dealer  for  the  purpose  of  looking  over 
the  various  makes  of  plows  might  be  a  profitable  exercise.  The 
manufacturer's  and  the  dealer's  viewpoint  is  as  valuable  as  that 
of  the  farmer. 


CHAPTER  V 
ORGANIC  MATTER 

A  very  important  constituent  of  soil  is  the  more  or  less 
decomposed  organic  matter  that  has  become  incorporated 
with  it.  Organic  matter  is  found  in  larger  quantity  in  sur- 
face-soil than  in  subsoil  because  it  comes  largely  from  vege- 
table matter  that  has  fallen  on  the  surface  and  there  decayed, 
or  that  has  been  plowed  under.  Animal  remains  and  lower 
forms  of  plant  life  also  contribute  to  the  supply.  The  roots 
of  dead  plants  are  one  source  of  organic  matter,  and  as  these 
generally  penetrate  into  the  subsoil  they  deposit  a  limited 
quantity  of  organic  matter  in  that  part  of  the  soil. 

50.  Classes  of  organic  matter.  —  Organic  matter  that 
is  incorporated  with  soil  gradually  decomposes,  forming 
substances  that  are  very  different  in  their  properties  from 
the  original  material.  The  process  may  be  roughly  divided 
according  to  the  degree  of  decomposition  into  three  classes, 
viz :  (1)  undecomposed  matter,  (2)  partially  decomposed 
matter,  (3)  final  products.  The  substances  representing 
each  of  the  stages  in  the  process  have  different  properties 
and  differ  in  their  effect  on  soil. 

Undecomposed  organic  matter  is  of  use  in  making  less 
compact  a  heavy  soil ;  on  the  other  hand,  it  may  make  too 
loose  a  naturally  light  soil  and  may  cause  it  to  dry  out  to 
such  an  extent  that  its  productiveness  will  be  curtailed. 
For  instance,  a  stand  of  oat  stubble  or  of  corn  stalks  that 
would  be  of  much  benefit  to  a  heavy  soil  in  a  humid  region 
might  injure  seriously  a  light  soil  in  a  semi-arid  region. 

51 


52  SOILS  AND   FERTILIZERS 

Partially  decomposed  organic  matter  is  of  benefit  to  soils 
in  a  number  of  ways  and  it  may  also  be  injurious.  These 
properties  will  be  discussed  later.  The  term  " humus" 
has  been  somewhat  loosely  used  with  reference  to  the  sub- 
stances of  this  class.  It  will  not  be  used  in  this  book. 
Organic  substances  represent  a  wide  range  of  intermediate 
products  of  decomposition.  They  profoundly  affect  the 
properties  of  soils  and  are  always  present  in  arable  soils. 

Final  products  of  decomposition  of  organic  matter  are 
water  and  gases.  The  latter  may  unite  with  some  of  the 
inorganic  matter  of  the  soil  to  form  purely  inorganic  sub- 
stances, and  these  are  as  a  rule  readily  available  to  plants. 
They  differ  from  the  substances  of  the  other  two  classes  in 
that  none  of  them  is  injurious  to  crop  production. 

51.  Beneficial  effects  of  organic  matter.  —  There  are 
many  ways  in  which  organic  matter  may  benefit  soils,  either 
directly  or  indirectly.  Soils  differ  somewhat  in  the  effect 
that  organic  matter  may  have  on  some  of  their  properties. 
An  example  of  this  has  been  cited  in  the  effect  of  organic 
matter  on  a  heavy  soil  in  a  humid  region  as  compared  with 
its  results  in  a  light  soil  in  a  semi-arid  region.  Another 
example  is  to  be  found  in  the  results  that  follow  the  plowing 
under  of  green-manures.  In  some  soils  and  under  certain 
conditions  this  may  be  temporarily  injurious,  although  it 
is  usually  a  very  beneficial  practice. 

An  enumeration  of  the  beneficial  effects  of  organic  matter 
in  soil  is  necessarily  open  to  criticism  on  account  of  the  dif- 
ferent responses  of  different  soils,  but  with  some  modifications 
the  following  will  hold. 

(1)  It  increases  the  tendency  towards  the  formation  of 
granular  structure. 

(2)  On  account  of  the  porous  nature  of  organic  matter 
the  pore  space  of  the  soil  is  increased  and  aeration  improved. 

(3)  It  increases  the  water-holding  capacity  of  soils. 


ORGANIC   MATTER  53 

(4)  It  improves  drainage  by  reason  of  the  properties 
stated  under  (1)  and  (2). 

(5)  It  increases  the  extent  of  root  growth  for  the  same  rea- 
sons. 

(6)  By  making  the  soil  darker,  it  facilitates  heat  absorp- 
tion. 

(7)  It  is  a  source  of  plant-food  material. 

(8)  It  furnishes  energy  for  the  growth  of  bacteria. 

(9)  Its  decomposition  produces  carbonic  acid  gas  and 
other  acids  that  help  to  render  plant-food  materials  soluble. 

52.  Porosity  of  organic  matter.  —  The  way  in  which  or- 
ganic matter  promotes  a  granular  structure  in  soils  has 
already  been  described,  as  has  also  the  relation  of  soil  struc- 
ture to  tilth.  In  addition  to  this  effect  on  soils,  organic 
matter  also  serves  to  make  soil  more  porous  by  reason  of 
its  own  porosity.  It  may  be  compared  to  a  sponge  in  its 
ability  to  hold  air  or  water.  A  peat  soil,  for  instance,  will 
hold  more  water  than  its  own  weight  of  dry  matter.  Or- 
ganic matter  extracted  from  a  peat  soil  was  found  to  carry 
twelve  times  its  own  weight  of  water.  It  may  readily  be 
seen  that  the  porous  nature  of  this  organic  matter  may 
greatly  increase  the  water-holding  capacity  of  a  soil.  At 
the  same  time  it  may  increase  the  capacity  of  the  soil  for  air. 

53.  Organic  matter  and  drainage.  —  By  reason  of  the 
greater  porosity  due  to  the  presence  of  organic  matter,  the 
movement  of  water  through  soils  is  facilitated  and  thus  the 
soil  is  better  drained.  The  advantages  of  good  drainage 
will  be  discussed  more  fully  later,  but  an  important  one 
of  these  is  a  greater  growth  of  roots,  which  increases  their 
opportunity  for  securing  food  and  thus  increases  the  size  of 
crop. 

54.  Organic  matter  and  soil  color.  —  Partly  decomposed 
organic  matter  generally  gives  a  dark  color  to  a  soil.  A 
dark  soil  absorbs  heat  more  readily  than  does  a  light-colored 


54  SOILS   AND   FERTILIZERS 

one,  and  as  warmth  is  an  important  factor  in  plant  growth, 
especially  in  the  spring,  a  dark  soil  usually  has  an  advantage 
over  a  light-colored  one. 

55.  Organic  matter  a  carrier  of  plant-food  material.  — 
In  its  relation  to  the  supply  of  plant-food  material,  organic 
matter  is  the  storehouse  in  which  nitrogen  is  held  in  a  form 
in  which  it  cannot  be  leached  from  the  soil  in  large  amounts 
and  yet  from  which  it  gradually  becomes  available  to  plants. 
Certain  inorganic  plant  nutrients  are  likewise  held  in  such 
condition  that  they  readily  become  useful  to  plants.  In  the 
process  of  rotting,  combinations  are  formed  between  organic 
matter  and  certain  inorganic  plant  nutrients,  removing  the 
latter  from  the  very  insoluble  minerals  of  the  soil.  On 
further  decomposition  the  inorganic  substances  are  left  in  a 
form  readily  usable  by  plants. 

56.  Organic  matter  and  nitrogen.  —  The  relation  of 
organic  matter  to  the  nitrogen  supply  is  of  particular  inter- 
est because  it  is  as  organic  matter  that  practically  the  entire 
supply  of  nitrogen  enters  the  soil.  All  soil  nitrogen  has  been 
secured  from  the  air  and  the  process  is  still  going  on.  This 
is  done  largely  by  the  lower  forms  of  plant  life  known  as 
bacteria,  fungi  and  molds.  These  organisms  living  in  the 
soil,  or  in  the  roots  of  higher  plants,  feed  on  the  non-nitrog- 
enous organic  matter  of  the  soil  and  plants,  and  upon  the 
nitrogen  of  the  atmosphere  that  passes  into  the  pores  of  the 
soil.  The  non-nitrogenous  organic  matter  and  the  atmos- 
pheric nitrogen  are  thus  combined  to  form  the  tissues  of 
these  lower  plants,  which  soon  die  and  finally  add  to  the 
soil  the  nitrogen  they  have  accumulated. 

57.  Organic  matter  and  soil  microorganisms. — We  have 
just  seen  how  the  nitrogen-fixing  organisms  use  non-nitrog- 
enous organic  matter  in  their  growth.  They  use  it  as  a 
source  of  energy,  as  do  animals.  Many  other  forms  of  lower 
plant  life  use  organic  matter,  both  nitrogenous  and  non- 


ORGANIC   MATTER  55 

nitrogenous.  As  the  growth  of  these  organisms  is  very- 
necessary  in  making  the  various  sorts  of  plant  nutrients 
available,  the  supply  of  organic  matter  for  this  purpose  is 
of  great  importance. 

58.  Organic  matter  forms  acids.  —  Finally,  organic  matter 
in  its  very  last  stages  of  decomposition  continues  to  serve 
the  plant  by  producing  carbonic  acid  gas,  which,  dissolved 
in  soil  water,  is  an  excellent  solvent  for  many  mineral  sub- 
stances needed  by  plants.  It  is  estimated  that  in  an  acre 
of  soil  sixteen  inches  deep,  sixty-eight  pounds  of  carbon 
dioxide  are  produced  annually  from  the  decomposition  of 
organic  matter  when  present  in  ordinary  quantity.  There 
are  also  other  organic  acids  formed  by  the  rotting  of  or- 
ganic matter  that  serve  to  dissolve  the  inorganic  matter  of 
soils.  The  combinations  of  these  organic  acids  with  min- 
eral substances  form  readily  available  plant-food  materials. 
Another  final  product  of  nitrogenous  organic  matter  is 
nitrate,  which  is  the  most  'available  form  of  nitrogen  for 
many  plants. 

59.  Injurious  effect  of  organic  matter.  —  The  injury  that 
organic  matter  may  cause  is  probably  not  of  very  frequent- 
occurrence  and  is  unimportant  as  compared  with  its  benefi- 
cial action.     Two  effects  have  been  noted  : 

(1)  Undecomposed  organic  matter  may  cause  a  soil  to 
dry  out  quickly  by  preventing  it  from  settling  sufficiently 
to  establish  water  connection  with  the  subsoil  and  by  leav- 
ing large  air  spaces  that  allow  a  rapid  movement  of  air 
through  them  which  dries  out  the  soil. 

(2)  Partially  decomposed  organic  matter  may  form  prod- 
ucts that  are  poisonous  to  some  agricultural  plants  or  that 
interfere  with  the  operations  of  those  microorganisms  that 
are  beneficial  to  plant  growth. 

60.  Management  of  soil  with  respect  to  organic  matter.  — 
The  first  step  in  the  control  of  organic  matter  in  soil  is  to 


56 


SOILS  AND   FERTILIZERS 


bring  about  decomposition,  which  operation  is  performed 
by  bacteria,  fungi  and  molds.  It  has  already  been  pointed 
out  that  unrotted  organic  matter  has  very  little  useful- 


Fig.  10.  —  The  upper  figure  represents  a  furrow  slice  laid  too  flat  for  the 
most  rapid  decay  of  organic  matter  when  present  in  large  quantity.  The 
lower  illustration  shows  a  better  furrow  angle. 

ness  and  may  be  injurious.  The  conditions  that  favor  the 
rapid  and  desirable  rotting  of  organic  matter  are  the  fol- 
lowing : 

(1)  An  amount  of  moisture  that  will  not  fill  all  of  the 
pore  spaces,  but  that  will  provide  water  required  by 
the  organisms  that  decompose  the  organic  matter.  The 
soil  moisture  content  most  favorable  for  plant  growth  is 
about  the  same  as  that  most  favorable  for  rotting  organic 
matter. 

(2)  The  soil  should  be  loose  enough  to  allow  air  to  pene- 
trate readily,  but  not  so  loose  as  to  leave  large  air  spaces. 
Air  is  necessary  to  the  activity  of  those  organisms  that  pro- 
duce a  desirable  kind  of  decomposition.  A  compact  soil, 
or  a  very  wet  soil  delays  the  rotting  process  and  favors  the 
growth  of  organisms  that  form  products  poisonous  to  agri- 
cultural plants. 


ORGANIC   MATTER  57 

(3)  The  soil  should  not  lack  lime,  as  the  presence  of  lime 
in  a  readily  soluble  form  favors  the  development  of  many 
forms  of  life  that  decompose  organic  matter,  and  it  also 
prevents  the  poisonous  action  of  certain  substances  pro- 
duced in  the  process. 

61.  Sources  of  organic  matter.  —  In  addition  to  the 
natural  supply  of  organic  matter  referred  to  in  the  first  part 
of  this  chapter,  there  are  other  sources  from  which  the 
farmer  may  obtain  a  supply  by  outright  purchase  or  by 
means  of  their  production  on  the  farm.  Among  these  are 
farm  manure,  grass  and  clover  sod,  green-manures,  peat  and 
muck,  crop  residues,  like  straw,  cornstalks  and  leaves,  dead 
animals,  certain  commercial  products,  like  cottonseed  meal 
and  dried  blood,  and  finally  weeds,  which  are  sometimes  used 
for  that  purpose  in  orchards. 

These  various  materials  and  their  use  in  contributing  to 
the  supply  of  organic  matter  in  soils  will  be  discussed  later 
under  the  respective  heads  (1)  farm  manure,  (2)  green- 
manures  and  (3)  commercial  fertilizers. 

QUESTIONS 

1.  Into  what  three  classes  may  the  organic  matter  of  the  soil  be 
divided  ?    . 

2.  What  is  the  effect  of  organic  matter  on  the  water-holding 
capacity  of  soil  ? 

3.  What  is  the  effect  of  organic  matter  on  drainage  ? 

4.  How  does  organic  matter  contribute  to  the  availability  of 
plant  nutrients  in  soils  ? 

5.  In  what  general  way  does  organic  matter  affect  the  growth  of 
bacteria  in  soils  ? 

6.  How  do  the  final  products  in  the  decomposition  of  organic 
matter  increase  the  availability  of  plant-food  materials  in  soil  ? 

7.  In  what  two  ways  may  organic  matter  be  injurious  to  soils  ? 

8.  What  are  the  soil  conditions  that  favor  a  rapid  and  desirable 
decomposition  of  organic  matter  ? 

9.  Name  the  sources  of  organic  matter  that  may  serve  to  increase 
the  supply  in  soils. 


58 


SOILS   AND   FERTILIZERS 


LABORATORY   EXERCISES 

Exercise  I.  —  Examination  of  soil  for  organic  matter. 
Materials.  —  Samples  of  clay  soils  respectively  low  and  high 
in  organic  matter,  hand  lens,  flame. 

Procedure.  —  Examine  a  soil  rich  in  organic  matter  under  the 
hand  lens.  Observe  character  of  the  organic  matter,  its  color  and 
its  effect  on  structure.  Compare  the  structure  of  the  soils  high  and 
low  in  organic  matter.  What  effect  does  the  organic  matter  ap- 
pear to  have  upon  granulation  ?  How  should  the  organic  matter 
influence  the  ease  of  preparing  a  seed  bed?  How  does  organic  matter 
influence  percolation  of  water  through  a  soil  ?  How  does  it  affect  its 
water  capacity  ? 

Place  a  small  portion  of  the  soil  rich  in  organic  matter  in  the 
flame.     Observe  and  explain  the  results. 

Exercise  II.  —  Examination  of  peat  and  muck. 
Materials.  —  Samples  of  peat  and  muck,  hand  lens,  flame. 

Procedure.  —  Examine  samples 
under  lens  and  describe  and  make 
drawings.  What  is  the  origin  of 
the  materials,  their  structure,  com- 
position and  degree  of  decay  ? 
What  is  the  value  of  peat  and 
muck  ? 

Place  a  small  portion  of  each  in 
the  flame.  Observe  and  explain 
results.  What  is  shown  regarding 
the  composition  of  peat  and  muck  ? 

Exercise  III.  —  Estimation  of 
organic  matter. 

Materials.  —  Soil  samples,  cru- 
cible, stirring  wire,  flame,  tripod, 
clay  triangle,  balance. 

Procedure.  —  Place  a  five-gram 
sample  of  dry  soil  in  a  weighed 
crucible.  Ignite  with  frequent 
stirrings  at  a  low  red  heat  over  a  flame  until  original  dark  color  has 
disappeared.  Cool  and  weigh.  The  loss  has  been  largely  organic 
matter.  Calculate  the  percentage  based  on  the  original  sample. 
Find  in  this  way  the  percentage  of  organic  matter  present  in  several 
different  soils. 


Fig.  11.  —  Apparatus  for  the  esti- 
matiqn  of  organic  matter  in  soil. 
(A)  crucible,  (B)  clay  covered  tri- 
angle, (C)  tripod,  (D)  Bunsen  burner. 


ORGANIC   MATTER 


59 


Exercise  IV.  —  Extraction  of  partly  decomposed  organic  matter. 

Materials.  —  Muck,  dilute  hydrochloric  acid,  ammonia,  hydrate 
of  lime,  filter  paper  and  funnel. 

Procedure.  —  Place  about  a  gram  of  moist  muck  on  a  filter  paper 
in  a  funnel.  Treat  the  muck  with  a  few  drops  of  dilute  hydrochloric 
acid.  Wash  out  the  acid  with  50  c.c.  of  distilled  water.  Discard 
this  percolation.  Now  treat  the  soil  with  ammonia.  After  allow- 
ing it  to  stand  a  few  minutes  wash  with  distilled  water  and  catch 
percolate. 

The  percolate  should  be  black,  showing  the  presence  of  partly  de- 
composed organic  matter.  This  is  the  material  seen  escaping  from 
manure  piles.     It  is  the  most  valuable  portion  of  the  organic  matter. 

Treat  a  portion  of  this  soluble  organic  matter  with  hydrate  of 
lime.  Note  the  flocculating  effect,  which  prevents  the  leaching  of 
organic  matter  from  the  soil. 

Exercise  V.  —  Influence  of  organic  matter  on  rate  of  percola- 
tion of  water  through  soils. 


Fig.  12.  —  Apparatus  for  studying  the  influence  of  the  addition  of  organic 
matter  to  a  soil  on  the  rate  of  percolation  and  percentage  of  water  holding 
capacity. 

Materials.  —  Clay  or  clay  loam  soil  finely  pulverized,  moist 
muck,  lamp  chimneys,  torsion  balance  and  weights,  cheesecloth. 

Procedure.  —  Divide  the  soil  in  two  portions.  To  one  add  10  per- 
cent of  the  moist  muck.     Mix  thoroughly.     Place  equal  and  definite 


60  SOILS   AND   FERTILIZERS 

weights  of  the  two  portions  of  soil  in  respective  lamp  chimneys, 
having  previously  tied  cheesecloth  neatly  over  the  bottoms  to  keep 
the  soil  in  place  and  yet  to  allow  drainag3.  Compact  the  soils  to 
uniform  height.  Weigh  each  chimney  plus  its  portion  of  soil. 
Set  the  chimneys  in  such  a  position  as  to  allow  free  drainage.  Pour 
equal  amounts  of  water  on  each  and  observe  the  rate  of  percolation 
of  the  water  through  the  two  soils.  Explain  results  and  show  the 
practical  bearing  of  the  experiment. 

Exercise  VI.  —  Influence  of  organic  matter  on  percentage  of 
moisture  held  in  soil. 

Materials.  —  Same  as  Exercise  V. 

Procedure.  —  After  observing  the  rate  of  percolation  in  the 
above  exercise,  saturate  the  soils,  and  allow  them  to  drain  freely 
until  all  gravity  water  has  disappeared.  Now  weigh  each  chimney 
plus  its  soil.  The  increased  weight  over  that  of  the  original  sample 
is  water  retained.  Calculate  the  percentage  of  water  thus  re- 
tained, based  on  the  weight  of  the  original  dry  sample.  Explain 
the  practical  importance  of  the  results. 


CHAPTER  VI 
SOIL  WATER 

Of  the  great  number  of  factors  that  influence  the  growth 
of  crops  none  is  of  more  importance,  or  possibly  of  as  much 
importance,  in  its  effect  on  the  yield  of  crops  as  water.  A  soil 
may  contain  too  much  water  for  the  best  growth  of  crops,  or 
it  may  have  too  little.  On  the  one  hand,  we  approach  swamp 
conditions,  and  on  the  other  the  desert  state.  Even  in  the 
same  locality  and  with  equal  rainfall  one  field  may  have 
too  much  moisture  and  another  too  little.  While  the  volume 
of  water  contained  in  a  soil  depends  more  or  less  on  the  rain- 
fall, it  is  not  controlled  entirely  by  it;  for  within  a  wide 
range  of  atmospheric  precipitation  soils  of  the  same  type 
may  not  vary  greatly  in  their  moisture  content.  This  is 
because  there  are  other  factors  beside  rainfall  that  serve 
to  regulate  the  supply  of  soil  water. 

62.  Forms  of  water  in  soils.  —  It  has  already  been  pointed 
out  that  in  every  soil  there  are  spaces  between  the  particles, 
or  aggregates  of  particles  and  that  the  size  and  total  volume 
of  these  spaces  vary  with  different  soils.  These  spaces 
may  be  completely  filled  with  water  or  they  may  be  nearly 
empty.  When  the  pore  spaces  are  entirely  filled  with  water, 
three  forms  of  water  are  found  to  be  present :  (1)  hygro- 
scopic, (2)  capillary  and  (3)  free  or  gravitational.  These 
forms  differ  in  their  relation  to  the  soil  particles. 

63.  How  the  three  forms  of  water  differ.  —  No  soil  in  a 
natural  state,  that  is  as  it  exists  in  the  fields  or  woods,  is 
ever  perfectly  dry.     No  matter  how  small  the  rainfall  or  how 

61 


62  SOILS   AND   FERTILIZERS 

parched  the  crops,  there  is  always  a  thin  film  of  moisture 
surrounding  each  particle  or  aggregation  of  particles,  al- 
though plants  may  not  be  able  to  obtain  it.  The  thin  film 
that  is  absorbed  from  the  air  and  condensed  on  the  surfaces 
of  the  particles,  when  no  other  source  of  supply  is  at  hand, 
is  termed  hygroscopic  water.  If  the  film  becomes  somewhat 
thicker  by  reason  of  another  supply  like  rainfall  or  under- 
ground water,  the  additional  supply  is  termed  capillary 
water.  These  two  forms  are  much  alike,  both  being  held 
as  a  film  around  the  particles,  partly  by  the  attraction  of  the 
soil  for  the  water  and  partly  by  the  attraction  of  the  particles 
of  the  water  for  each  other,  which  prevents  the  film  from 
breaking  and  running  away.  One  other  difference  between 
hygroscopic  water  and  capillary  water  is  that  the  former  is 
always  stationary,  while  the  latter  may  move. 

A  further  increase  in  the  quantity  of  water  in  a  soil  gives 
rise  to  the  third  form  —  gravitational  or  free  water.  With 
the  advent  of  more  water,  the  films  become  so  thick  that 
the  attraction  by  which  they  adhered  to  the  particles  is 
overcome  by  gravity  and  there  is  a  downward  movement 
through  the  pore  spaces,  or  else  the  pore  spaces  are  com- 
pletely filled  and  the  soil  becomes  saturated  by  reason  of 
the  inability  of  the  water  to  escape  from  the  soil. 

64.  Hygroscopic  water.  —  From  a  practical  viewpoint, 
hygroscopic  water  is  not  of  much  importance  because 
plants  cannot  use  it.  A  plant  may  die  for  want  of  water 
when  the  soil  in  which  it  grows  contains  its  maximum  of 
hygroscopic  moisture.  The  forces  that  hold  the  water  in 
the  soil  are  greater  than  those  that  tend  to  draw  it  into 
the  plant. 

The  quantity  of  hygroscopic  moisture  that  a  soil  will 
hold  depends  largely  on  its  texture  and  on  the  quantity  of 
partially  decomposed  organic  matter  that  it  contains.  Fine 
particles  have  a  greater  absorptive  power  for  water  than  do 


SOIL    WATER  63 

coarse  ones.  Clay  has  a  large  absorptive  capacity  and 
the  presence  of  certain  compounds  increases  immensely  the 
content  of  hygroscopic  moisture. 

65.  Capillary  water.  —  The  essential  difference  between 
capillary  water  and  hygroscopic  water  is  that  the  former  is 
capable  of  motion  and  most  of  it  may  be  used  by  plants. 
The  fact  that  the  capillary  film  is 
thicker  causes  it  to  be  less  firmly  held 
by  the  soil  particles,  in  consequence  of 
which  the  water  near  the  outer  surface 
of  the  film  can  move  in  response  to 
certain  forces,  and  the  absorptive  ac- 
tion of  roots  is  sufficient  to  withdraw      FlG    13    _  Diagram_ 

it,  Until  the  film  becomes  SO  thin  that    matic  drawing  of  soil  par- 

very  little  except  hygroscopic  water  £^  ™^! 
remains.  The  difference  between  hy-  lary  water,  (s)  soil  parti- 
groscopic  water  and  capillary  water  is  ^^^^  ^ 
illustrated  in  Fig.  13. 

66.  Capillary  water  capacity.  —  Comparatively  large 
quantities  of  water  may  be  held  in  soils  by  capillarity.  In 
fact  by  far  the  major  portion  of  water  used  by  crops  is  ob- 
tained from  the  capillary  form.  The  quantity  present 
varies  with  different  soils  and  at  different  times  in  the  same 
soil.  The  conditions  that  tend  to  increase  the  capillary 
moisture  content  of  soil  are  the  following : 

LA  fine-grained  texture,  or  in  other  words  a  large  pro- 
portion of  small  particles.  Thus  in  a  test  of  a  fine  sand, 
a  sandy  loam  and  a  clay  soil  they  were  found  to  contain 
respectively  10,  15  and  20  percent  of  capillary  water  in 
addition  to  the  hygroscopic  water. 

2.  A  soil  structure  that  gives  a  maximum  effective  sur- 
face exposure  within  the  soil.  For  this  reason  the  granula- 
tion of  a  clay  soil,  or  the  compacting  of  a  coarse  sand  will 
cause  a  rise  in  its  capillary  capacity. 


64  SOILS   AND   FERTILIZERS 

3.  A  large  amount  of  partially  decomposed  organic  matter. 
Thus  a  muck  soil  may  contain  a  greater  weight  of  capillary 
water  than  the  weight  of  the  dry  soil  itself.  Farm  manure 
or  green-manures  are  valuable  for  this  purpose. 

4.  A  low  soil  temperature,  if  it  is  above  the  freezing  point. 

5.  A  strong  soil  solution,  such  as  is  produced  by  proper 
manuring  and  good  tillage. 

6.  The  absence  of  oily  material  produced  by  decay  of 
organic  matter. 

The  conditions  that  are  favorable  to  a  large  crop  pro- 
duction are,  in  general,  helpful  in  increasing  the  capillary 
water  capacity  of  a  soil.  The  effect  of  temperature,  and  of 
oily  material  formed  by  decay  of  organic  matter,  are  excep- 
tions to  this.  Much  may  be  done  by  tillage,  drainage  and 
manuring  to  increase  capillary  water  capacity. 

67.  Movement  of  capillary  water.  —  The  movement  of 
capillary  water  is  from  particle  to  particle  within  the  water 
film,  the  film  being  continuous  from  one  particle  to  the  other. 
The  movement  is  always  from  the  thicker  part  of  the  film 
to  the  thinner  part,  because  there  is  a  tendency  for  the  film 
to  assume  the  same  thickness  throughout.  Capillary  move- 
ment may,  therefore,  be  upward  or  downward  or  lateral. 
Following  a  shower  of  rain  the  movement  is  downward,  as 
there  is  more  moisture  at  the  surface  than  below.  Generally 
the  movement  during  the  growing  season  is  from  the  lower 
soil  towards  the  surface,  because  the  roots  and  surface  evapo- 
ration continually  remove  water  from  the  upper  part  of  the 
soil  and  this  is  replenished  from  the  wetter  soil  below.  The 
lateral  movement  is  usually  slight.  The  factors  that  deter- 
mine the  rate  of  movement  of  capillary  water  are  much  the 
same  as  those  that  influence  its  quantity.  They  are 
(1)  texture,  (2)  structure,  (3)  height  of  water  column,  and 
to  a  less  extent  the  other  factors  that  influence  the  quantity 
of  capillary  water. 


SOIL    WATER 


65 


68.  Effect  of  texture  on  capillary  movement.  —  The  finer 
the  texture  of  a  soil,  other  things  being  equal,  the  slower 
is  the  movement  of  capillary  water,  but  the  water  will 
eventually  rise  higher  in  the  soil  of  fine  texture.  This  is 
illustrated  by  the  experimental  data  contained  in  the  fol- 
lowing table : 

Table    12.  —  Effect   of   Texture    on   Rate    and    Height    of 
Capillary  Rise  from  a  Water  Table  through  Dry  Soil 


Soil 

1  Hour 

1  Day 

2  Days 

3  Days 

4  Days 

5  Days 

inches 

inches 

inches 

inches 

inches 

inches 

Sand .     .     .     .     . 

3.5 

5.0 

5.9 

6.8 

6.8 

6.9 

Clay 

.5 

5.7 

8.9 

10.9 

12.2 

13.3 

Silt 

2.5 

14.5 

20.6 

24.2 

26.2 

27.4 

One  can  see  from  the  above  data  that  although  water  rises 
most  rapidly  in  the  sand,  it  does  not  rise  as  high  as  in  the 
other  soils.  This  experiment  was  not  continued  long  enough 
to  obtain  the  maximum  rise  in  clay.  Some  experimenters 
have  been  able  to  obtain  a  rise  of  water  to  a  height  of  twenty- 
six  feet  in  a  clay  soil. 

69.  Effect  of  structure  on  capillary  movement.  —  Soil 
structure  by  affecting  the  size  of  the  pore  spaces  also  affects 
the  rate  of  capillary  movement.  In  general  the  condition 
most  favorable  for  plant  growth  is  also  best  adapted  to 
capillary  movement.  Good  tillage,  tile  drainage,  farm 
manure  and  lime  all  help  to  hasten  the  movement  of  water 
in  a  soil.  A  very  loose  soil  does  not  admit  of  capillary  move- 
ment and  consequently  cultivation  of  the  surface  prevents 
water  from  coming  to  the  surface  of  the  ground  from  whence 
it  escapes  into  the  air.  Rolling,  or  otherwise  compacting 
the  soil  aids  capillary  movement  and  thus  causes  loss  of 
moisture  from  the  surface  soil. 


66  SOILS   AND   FERTILIZERS 

70.  Height  of  water  column  and  capillary  movement. — 
Gravity  opposes  the  upward  movement  of  water  and  conse- 
quently the  higher  water  rises  the  more  slowly  it  moves. 
This  has  been  demonstrated  by  measuring  the  quantity  of 
water  that  evaporated  from  the  surface  of  columns  of  sand 
of  different  heights,  the  rate  of  loss  by  evaporation  indicat- 
ing the  degree  of  rapidity  of  movement. 

Table  13.  —  Evaporation  from  the  Surface  of  Sand  Columns 

of  Different  Heights,  their  Bases  being  in  Contact  with 

Free  Water 


Height  of  Column 
in  Inches 

Daily  Evaporation  at  Surface  in 
Pounds  per  Acre 

6 

25,872 

25,191 

18,155 

7,716 

4,312 

12 

18 

24 

30 

This  has  a  practical  significance  in  dry  weather  when  the 
moisture  supply  for  plants  is  drawn  largely  from  the  water 
stored  in  the  lower  soil.  The  lower  the  water  level  becomes, 
the  more  slowly  does  the  moisture  rise  to  the  surface  soil  where 
are  to  be  found  the  larger  part  of  the  roots  of  many  plants. 
Fortunately,  however,  as  the  soil  dries  out,  the  roots  go  some- 
what deeper,  so  that  they  in  part  overcome  this  difficulty. 

71.  Gravitational  water.  —  It  has  already  been  said  that 
gravitational,  or  free  water,  is  the  water  in  excess  of  the  cap- 
illary water  and  is  constantly  moving  downward,  thus  pre- 
venting the  soil  from  becoming  saturated  owing  to  the 
inability  of  the  water  to  escape.  It  is  very  desirable  that 
the  gravitational  water  shall  not  remain  in  that  part  of 
the  soil  in  which  plants  have  their  roots.  A  saturated 
condition  of  the  surface  soil  is  very  injurious  to  most  agri- 
cultural plants.     In  this  respect  there  is  a  great  difference 


SOIL   WATER  67 

between  gravitational  water  and  capillary  water,  and  while 
it  is  desirable  to  have  as  much  capillary  water  as  possible 
in  the  soil  at  all  times,  it  is  equally  important  that  the  gravi- 
tational water  shall  be  removed. 

The  factors  that  determine  the  rate  of  flow  of  gravitational 
water  in  soil  are  texture,  structure,  and  cracks  and  openings 
produced  by  freezing,  by  drying,  by  roots  and  by  the  bur- 
rowing of  sundry  forms  of  animal  life,  like  worms  and 
insects.  Another,  and  very  important  factor,  is  the  means 
for  the  escape  of  water  from  the  subsoil,  since  without  that  a 
soil  will  become  saturated  no  matter  how  favorable  the 
conditions  may  be  for  escape  of  water  from  the  surface 
soil.     For  this  purpose  tile  drainage  must  often  be  used. 

A  sandy  soil  allows  the  escape  of  gravitational  water  more 
rapidly  than  does  a  loam  or  clay  soil.  Soil  in  good  tilth  is 
better  in  this  respect  than  is  compact  soil.  It  is  better 
that  water  should  run  through  a  soil  than  that  it  should  run 
off  the  surface.  The  latter  generally  causes  erosion  with  the 
loss  of  much  good  soil,  and  may  leave  the  subsoil  too  dry. 
For  this  reason  a  loam  or  clay  soil  should  always  have  a 
loose  surface  when  no  crop  is  on  the  ground. 

72.  The  water  table.  —  The  gravitational  water  that 
passes  through  the  ground  accumulates,  in  humid  regions, 
in  the  lower  depths  of  soil,  or  possibly  in  underlying  sand 
or  gravel,  which  it  saturates.  The  surface  of  this  mass  of 
water  is  called  the  water  table,  the  depth  of  which  below 
the  surface  of  the  ground  varies  from  a  few  inches  to  a  great 
many  feet,  depending  on  the  opportunity  it  has  to  escape. 
This  is  the  water  that  furnishes  the  supply  for  shallow  wells 
and  for  springs.  In  some  places  the  water  table  is  sufficiently 
near  the  surface  to  be  of  use  to  plants  owing  to  its  capillary 
rise  during  dry  periods. 

73.  Relations  of  soil  water  to  plants.  —  The  quantities 
and  movements  of  the  several  forms  of  water  in  soils  are  of 


68  SOILS   AND   FERTILIZERS 

the  greatest  importance  in  the  growth  of  plants.  There  are 
certain  more  or  less  definite  relations  that  obtain,  so  that 
for  any  given  condition  of  the  water  supply  certain  results 
in  crop  growth  may  be  expected.  As  we  shall  see  later, 
these  conditions  of  water  supply  are,  within  certain  limits, 
subject  to  the  control  of  man  and  consequently  the  growth 
of  crops  may  be  regulated  to  some  extent  by  these  means. 

74.  Ways  in  which  water  is  useful  to  plants.  —  In  many 
indirect  ways  water  contributes  to  plant  growth,  as  for 
instance  in  aiding  in  the  disintegration  of  rocks,  in  the  pro- 
motion of  decay  of  organic  matter  and  in  numerous  other 
ways,  but  it  is  with  the  use  of  water  as  it  occurs  in  soils  and 
as  taken  up  by  plants  that  we  are  now  concerned.  The 
functions  that  water  thus  serves  may  be  listed  as  follows : 

1.  Water  is  a  direct  source  of  food  material,  for  it  either 
becomes  a  part  of  the  plant  substances  without  change  (about 
90  percent  of  most  plants  is  water),  or  it  is  decomposed  and 
its  elements  are  used  in  building  plant  tissue. 

2.  Water  acts  as  a  solvent  and  carrier  of  plant-food  ma- 
terials, taking  up  these  substances  in  the  soil  and  transferring 
them  to  the  plant,  where  they  are  utilized  in  the  formation 
of  plant  tissue. 

3.  Water  in  the  plant  serves  to  keep  the  cells  expanded, 
to  regulate  the  temperature  and  to  carry  in  solution  sub- 
stances from  those  portions  of  the  plant  in  which  they  are 
formed,  to  the  places  where  they  are  needed,  as  for  instance, 
to  transport  soluble  matter  from  the  leaves  of  the  potato, 
where  the  starch  is  formed,  to  the  tuber,  where  it  is  stored. 

75.  Water  requirements  of  plants.  —  Most  of  the  water 
that  enters  the  roots  passes  on  through  the  plant  and  evapo- 
rates from  openings  in  the  leaves.  A  large  crop  will,  other 
things  being  equal,  require  more  water  for  its  production 
than  a  small  crop.  The  ratio  of  the  quantity  of  water  used, 
to  the  quantity  of  dry  matter  that  the  plants  contain,  is 


SOIL    WATER  69 

called  the  transpiration  ratio,  because  the  water  given  off 
by  the  leaves  of  the  plants  is  said  to  be  transpired.  The 
quantity  of  water  required  to  produce  a  pound  of  dry  matter 
varies  from  200  to  500  pounds  in  humid  regions  to  almost 
twice  that  amount  in  arid  regions.  There  are  a  number  of 
factors  that  influence  the  transpiration  ratio.  Among  these 
are  the  following : 

1.  The  kind  of  plant. 

2.  The  quantity  of  water  in  the  soil. 

3.  The  humidity,  wind  and  temperature  of  the  air. 

4.  The  natural  fertility  and  manurial  treatment  of  the  soil. 

76.  Transpiration  by  different  crops.  —  Some  kinds  of 
plants  require  much  more  water  to  produce  a  pound  of  dry 
matter  than  do  others.  Oats,  rye,  peas  and  potatoes  are 
crops  that  have  a  high  transpiration  ratio.  Wheat  and 
barley  have  medium  ratios  and  corn  and  millet  low  ratios. 
This,  in  a  way,  is  a  guide  to  the  adaptability  of  these  crops 
to  growth  on  dry  soils. 

77.  Effect  of  soil  moisture  on  transpiration.  —  An  increase 
in  the  water  content  of  any  soil  usually  results  in  an  increased 
transpiration  ratio  for  any  crop  grown  on  it.  This  is  well 
brought  out  by  an  experiment  in  which  corn  was  grown  in  soil 
contained  in  pots  to  which  different  quantities  of  water  were 
added  and  so  maintained  during  the  entire  period  of  growth  of 
the  plants.     The  results  are  expressed  in  the  following  table  : 

Table  14.  —  Effect  of  Soil  Moisture  on  Transpiration 


Soil  Moisture 

Transpiration 

Percentage  op  Total  Capacity 

Ratio 

100 

290 

80 

262 

60 

239 

45 

229 

35 

252 

70 


SOILS  AND   FERTILIZERS 


The  most  economical  utilization  of  water  was  secured  by 
a  medium  water  supply. 

78.  Effect  of  humidity,  wind  and  temperature  of  the  air. 
—  A  dry  atmosphere  and  a  high  temperature  increase  the 
transpiration  ratio.  For  this  reason  crops  require  a  large 
amount  of  water  in  arid  regions  and  in  regions  of  high  summer 
temperatures.  A  high  and  constant  wind  movement 
also  tends  to  raise  the  transpiration  ratio.  In  parts  of  the 
country  requiring  irrigation  the  economical  use  of  water  must 
be  considered.  Such  a  region  is  likely  to  have  much  sun- 
shine associated  with  high  temperatures  and  dry  atmosphere. 

79.  Effect  of  soil  fertility  on  transpiration.  —  A  soil  high 
in  available  plant-food  material  has,  in  general,  the  property 
of  producing  crops  with  a  small  unit  expenditure  of  water. 
Experiments  in  Nebraska  gave  the  following  results : 


Table  15.  —  Relative  Water  Requirements  of  Corn  on 
Different  Types  of  Nebraska  Soils 


Soil 

Dry  Weight  of 

Plants  in  Grams 

per  Pot 

Transpiration  Ratio 

Poor • 

113 
184 
270 

549 

Medium 

Fertile 

479 
392 

80.  Quantity  of  water  required  to  mature  a  crop.  —  A 
rough  estimate  of  the  quantity  of  water  required  to  bring 
to  maturity  a  crop  of  wheat  may  be  calculated  as  follows : 
Assuming  the  yield  to  be  forty  bushels  or  about  two  tons  of 
dry  matter  in  straw  and  grain  and  the  transpiration  ratio 
to  be  400,  the  quantity  of  water  actually  used  by  the  plants 
would  be  800  tons  to  the  acre,  or  equivalent  to  about  7 
inches  rainfall.  In  addition  to  this  there  would  be  an  equal 
or  larger  quantity  of  water  evaporated  directly  from  the 


SOIL   WATER  71 

soil.  The  annual  amount  of  rainfall  required  for  crop- 
production  is  brought  to  a  much  higher  figure  by  the  loss 
due  to  run-off  and  percolation. 

81.  Capillary  movement  and  plant  Requirement.  —  We 
have  seen  that  there  is  a  capillary  movement  of  water  from 
the  more  moist  to  the  less  moist  soil.  As  water  is  absorbed 
by  plants,  the  moisture  content  is  reduced  in  the  soil  sur- 
rounding the  root-hairs  by  which  the  moisture  is  taken  up. 
Immediately  a  movement  begins  to  establish  equilibrium 
in  the  water  films  and  during  the  time  the  roots  continue  to 
absorb  moisture,  the  movement  of  capillary  water  goes 
on.  During  the  blooming  period,  plants  must  have  very 
large  quantities  of  water  if  they  are  to  develop  fully  and 
produce  large  yields  of  grain.  Capillary  movement  is 
necessarily  slow,  especially  in  heavy  loam  and  clay  soils. 
It  is  often  impossible  for  the  capillary  movement  to  carry 
moisture  fast  enough,  except  for  short  distances,  to  supply 
plants  adequately  and  the  crop  suffers  for  want  of  moisture. 
In  a  dry  season  the  capillary  capacity  of  a  soil  is  likely  to 
be  of  more  importance  than  the  rate  of  capillary  movement, 
as  the  supply  is  more  easily  available.  Hence,  in  time  of 
drought  a  loam  soil  in  good  tilth  is  better  than  a  sandy 
soil. 

82.  Optimum  moisture  for  plant  growth.  —  Plants  wilt 
for  want  of  water  at  a  moisture  content  somewhat  higher 
than  that  represented  by  hygroscopic  moisture.  They 
show  the  pale  color  characteristic  of  too  much  moisture 
when  a  soil  is  saturated.  Before  either  of  these  well-known 
signs  of  distress  is  shown,  the  plant  may  have  too  much  or 
too  little  water  to  allow  of  its  maximum  growth.  The 
optimum  moisture  content  lies  somewhere  within  the  range 
of  capillary  moisture.  It  is  variously  stated  by  different 
experimenters  to  lie  between  60  and  90  percent  of  the  water 
capacity  of  soils.     Probably  it  varies  with  different  soils. 


72  SOILS  AND   FERTILIZERS 

The  range  is  doubtless  greater  for  a  soil  in  good  tilth  than 
for  one  in  poor  condition,  and  the  wider  the  range  of 
optimum  moisture  content  the  less  likely  is  a  crop  to  suffer 
from  either  extreme. 

83.  The  control  of  soil  moisture.  —  Since  there  may  be 
too  much  or  too  little  water  in  a  soil  for  its  most  effective 
crop  production,  the  problem  of  moisture  control  is  to  remove 
the  excess  and  to  conserve  the  remainder,  attempting  to 
maintain  the  supply  within  the  range  of  the  optimum  mois- 
ture content.  In  heavy  soils  there  is  likely  to  be  a  surplus 
of  water  in  the  spring  and  in  sandy  soils  a  deficit  in  midsum- 
mer. The  excessive  water  content  in  the  spring  is  also 
objectionable  because  it  delays  plowing,  planting,  and  germi- 
nation of  seed  as  well  as  the  early  growth  of  crops.  The 
ways  in  which  water  leaves  soil  are  by  (1)  run-off  over  the 
surface ;  (2)  percolation ;  (3)  evaporation ;  (4)  absorption  by 
plants.  The  last  of  these  is  to  be  encouraged,  at  least  when 
it  is  economically  accomplished.  Run-off  should  generally 
be  prevented.  Percolation  and  evaporation  should  be  con- 
trolled within  certain  limits. 

84.  Run-off.  —  Removal  of  water  in  this  way  is  objection- 
able because  the  rivulets  carry  with  them  the  fine  particles, 
which  are  frequently  the  most  valuable  part  of  a  soil,  and 
gullies  are  formed  that  may  interfere  with  the  working  of 
the  land.  In  regions  in  which  the  rainfall  is  large,  and 
particularly  where  it  falls  in  torrential  showers,  more  than 
half  of  the  precipitation  may  escape  in  this  way.  The 
water  so  removed  is,  of  course,  entirely  lost  so  far  as  its 
utilization  by  plants  is  concerned.  The  proportion  lost  by 
run-off  is  greater  on  slopes  than  on  level  land,  and  on  com- 
pact soil  than  on  sandy  soil  or  on  soil  in  good  tilth. 

The  removal  of  excess  water  by  means  of  open  ditches  is, 
to  some  extent,  a  utilization  of  run-off  to  drain  land,  but 
it  is  not  so  desirable  a  method  as  tile  drainage.     It  is  better 


Plate  VIII. 


Forms  of  Erosion.  —  Erosion  of  soil  by  water  in  upper 
figure.     Erosion  by  wind  in  lower. 


SOIL   WATER  73 

to  have  the  moisture  pass  into  the  soil  and  this  is  encouraged 
by  any  of  the  operations  and  conditions  that  favor  the  main- 
tenance of  good  tilth.  Fall  plowing  and  early  spring  plow- 
ing also  serve  this  end.  In  arid  and  semi-arid  regions  run- 
off is  usually  not  of  any  moment.  Terracing  a  hillside  is 
often  resorted  to  as  a  preventive  of  run-off,  especially  in 
the  south  Atlantic  states  where  the  rainfall  is  often  tor- 
rential. 

85.  Percolation.  —  Water  that  enters  a  soil  is  either 
retained  by  the  capillary  spaces  or  eventually  percolates 
into  the  subsoil.  The  percolate  is  lost  to  crops,  except  that 
part  which  remains  in  the  subsoil  and  is  later  raised  by 
capillarity  to  within  reach  of  roots.  The  chief  consideration 
is  to  maintain  the  soil  in  good  tilth,  which  gives  a  large 
capillary  capacity,  thus  storing  within  easy  reach  of  the 
roots  a  maximum  quantity  of  the  descending  water.  The 
more  rapidly  the  gravitational  water  is  disposed  of  the  better, 
because  its  presence  prevents  aeration  of  the  soil  together 
with  those  beneficial  processes  that  good  ventilation  encour- 
ages. One  of  the  most  frequent  causes  of  saturation  of  soil 
is  lack  of  facility  for  the  water  to  escape  from  the  lower 
depths.     This  difficulty  is  best  relieved  by  tile  drainage. 

86.  Evaporation.  —  It  has  been  concluded  from  experi- 
ments conducted  at  Rothamsted,  England,  that  with  an 
annual  rainfall  of  twenty-eight  inches,  one-half  is  lost  by 
percolation.  The  quantity  of  water  required  to  produce  an 
average  crop  in  a  humid  region  is  about  seven  inches,  which 
is  one-half  of  the  water  retained  by  the  soil.  The  other  half 
is  presumably  lost  by  evaporation.  A  rough  estimate  of 
the  disposition  of  rain  water  in  a  humid  region  would  there- 
fore be  one-half  lost  by  percolation,  one-fourth  by  evapora- 
tion and  one-fourth  used  by  the  growing  crop.  The  ratio 
of  quantity  lost  by  evaporation  to  quantity  used  by  crop 
may  vary  by  reason  of  a  number  of  factors,  among  which  is 


74  SOILS   AND   FERTILIZERS 

the  ease  with  which  evaporation  may  take  place.  Moisture 
saved  from  evaporation  is  at  the  immediate  disposal  of  the 
crop. 

87.  Mulches  for  moisture  control.  —  Any  material  ap- 
plied to  the  surface  of  a  soil  primarily  to  prevent  loss  by 
evaporation  may  be  designated  as  a  mulch.  It  may  at  the 
same  time  fulfill  other  useful  functions,  like  keeping  down 
weeds  and  maintaining  a  uniform  soil  temperature.  The 
mulch  ordinarily  used  for  fallow  land  is  produced  by  stirring 
the  surface  soil.  Mulches  may  be  formed  of  straw,  leaves, 
flat  stones,  cloth,  sawdust  and  various  other  materials,  but 
the  most  practical  material  is  soil. 

88.  The  soil  mulch.  —  The  soil  mulch  is  made  by  stirring 
the  surface  of  the  soil  with  some  one  of  the  ordinary  tillage 
implements.  For  fallow  land  a  disk  harrow,  straight,  or 
spring  tooth  harrow  may  be  used.  For  intertilled  crops 
numerous  forms  of  cultivators  are  made  for  the  special  pur- 
pose of  going  between  the  rows  of  plants.  For  small  grain 
a  weeder  or  spike-tooth  harrow,  with  the  teeth  slanted  back- 
ward, is  frequently  used  while  the  grain  is  young.  This 
practice  has  much  to  recommend  it  in  an  arid  or  semi-arid 
region. 

In  making  a  soil  mulch  the  object  is  to  destroy  the  capil- 
larity near  the  surface  soil  and  thus  to  prevent  the  move- 
ment to  the  surface  of  water  from  the  portion  of  the  soil 
below  the  mulch.  Stirring  may  accomplish  this  by  breaking 
up  the  cohesion  of  particles  to  such  an  extent  that  moisture 
cannot  pass  from  one  to  the  other. 

89.  Frequency  of  stirring.  —  Some  kinds  of  soil  re- 
quire more  frequent  stirring  than  others.  For  instance, 
a  sand  will  maintain  a  mulch  longer  than  a  loam  or  clay. 
The  latter  becomes  moist  from  below  and  will  gradually 
allow  moisture  to  reach  the  surface.  Rain  will  also  compact 
a  mulch  and  unless  it  is  soon  restored  there  may  be  more 


SOIL    WATER  75 

moisture  lost  than  was  received  as  rain.  While  it  is  not 
possible  to  make  a  definite  rule  for  frequency  of  stirring  a 
mulch,  it  may  be  said  that  a  mulch  should  never  be  allowed 
to  remain  in  a  compact  condition.  However,  in  arid  regions 
the  surface  of  the  soil  sometimes  becomes  completely  dry 
so  quickly,  even  when  compact,  that  capillary  connection 
is  destroyed  and  loss  of  moisture  is  prevented. 

90.  Depth  of  mulch.  —  In  considering  the  depth  that  a 
mulch  should  have,  several  facts  should  be  kept  in  mind. 
The  deeper  the  mulch  the  more  effective  it  will  be,  but  as 
it  must  be  perfectly  dry,  roots  cannot  obtain  nourishment  in 
the  zone  occupied  by  the  mulch.  The  surface  soil,  from 
which  plants  derive  a  large  part  of  their  material,  is  frequently 
only  eight  to  ten  inches  deep  in  humid  regions  and  the  deeper 
the  mulch  the  less  top  soil  remains  for  roots.  In  arid  regions 
plants  obtain  food  materials  from  greater  depths  and  mulches 
may  be  made  deeper,  which  is  fortunate  since  they  need  to 
be  deeper  in  regions  where  evaporation  is  greater.  Another 
consideration  is  the  disturbance  of  roots  in  the  process  of 
cultivation.  Here,  again,  there  is  less  occasion  to  cultivate 
shallow  in  an  arid  region,  as  roots  are  generally  found  at 
greater  depths  in  such  soils. 

A  good  depth  for  a  mulch  in  humid  regions  is  about  three 
inches,  becoming  somewhat  less  during  the  last  cultivations 
of  corn.  In  irrigated  regions  a  mulch  of  ten  to  twelve  inches 
is  frequently  used,  especially  in  orchards,  in  which  it  is  often 
not  necessary  to  renew  the  mulch,  as  the  rainfall  is  usually 
light. 

91.  Effectiveness  of  mulches.  —  That  mulches  are  effec- 
tive in  conserving  moisture  and  increasing  crop  yield  has 
lately  been  called  in  question  by  certain  writers  who  claim 
that  corn  is  not  more  benefited  by  tillage  than  by  the 
removal  of  weeds  without  tillage,  and  by  some  experi- 
menters who  find  that  fallow  land  contains  as  much  moisture 


76 


SOILS   AND   FERTILIZERS 


when  weeds  are  removed  by  scraping  the  surface  of  the 
ground  as  when  the  soil  mulch  is  maintained.  It  seems 
possible  that  the  latter  result  may  occur  only  in  those 
regions  in  which  conditions  are  such  that  a  natural  mulch  is 
formed  by  the  rapid  drying  of  the  surface  soil,  in  which 
process  moisture  is  removed  so  quickly  that  the  capillary 
column  is  broken  and  further  loss  of  moisture  is  stopped. 
This  would  confine  it  to  semi-arid  and  arid  regions  of  high 
summer  temperatures. 

The  failure  of  the  soil  mulch  to  conserve  moisture  in  corn 
land  has  been  explained  on  the  supposition  that  the  corn 
roots  ramifying  through  the  upper  soil  absorb  so  much 
water  that  they  cut  off  the  upward  movement  as  effectually 
as  does  a  mulch.  The  results  of  some  experiments  in 
semi-arid  Montana  indicate  a  high  degree  of  usefulness  for 
the  mulch. 

Table  16.  —  Moisture  Content  op  Mulched  and  Unmulched 
Eastern  Montana  Soils.     Average  of  Three  Years 


Depth  op  Sample 

Percent  Moisture  in  Soil  on  Oct  6. 

Mulched 

Unmulched 

Firstfoot 

16.8 

10.8 

Second  foot 

16.4 

9.4 

Third  foot 

13.2 

9.5 

Fourth  foot 

10.1 

8.9 

Fifth  foot 

9.6 

8.5 

Average 

13.2 

9.4 

The  investigator  comments  on  these  results  as  follows : 
"  If  the  wilting  point  of  this  soil  is  6  percent,  the  mulched 
area  contains  more  than  twice  as  much  available  moisture. 
This  3.8  percent  of  available  moisture  by  which  the  mulched 
soil  excels  the  unmulched  is  equivalent  in  a  five-foot  depth 
to  about  250  tons  of  water,  enough  to  increase  the  crop  by 
a  ton  of  dry  matter." 


SOIL    WATER 


77 


92.  Other  devices  to  prevent  evaporation.  —  Plowing  in  the 
early  spring  or  immediately  after  taking  off  a  crop  of 
small  grain  is  a  means  of  preventing  evaporation.     In  regions 


e&capino    moisture: 

3 1 f 1 


»l(SO     Mpl 


NO  MULCH 


Fig.  14.  —  The  effect  of  a  soil  mulch  is  to  break  up  the  capillary  spaces 
within  the  mulch  itself  and  thus  to  prevent  the  upward  movement  of  water 
through  it.  Water,  therefore,  remains  in  the  lower  soil  instead  of  evaporat- 
ing from  the  surface.  This  condition  is  shown  in  the  right-hand  column. 
When  no  mulch  is  maintained  the  soil  dries  at  the  surface  and  then  cracks, 
which  allows  it  to  dry  more  rapidly  below. 


in  which  grain  crops  suffer  for  moisture  in  the  early  spring, 
it  is  not  uncommon  for  farmers  to  harrow  the  small  grain, 
following  the  drill  rows  with  a  spike-tooth  harrow  with  its 
teeth  turned  backwards.  This  practice  is  likely  to  be  very 
beneficial. 


78  SOILS   AND   FERTILIZERS 

Windbreaks  are  effective  in  decreasing  evaporation  by 
lessening  the  velocity  of  the  wind.  King  found  that  evapora- 
tion from  a  moist  soil  was  twenty-four  percent  less  at  a  dis- 
tance of  twenty  to  sixty  feet  from  a  black  oak  grove  than  it 
was  about  three  hundred  feet  distant. 

93.  Rolling  and  subsurface  packing.  —  These  operations 
are  resorted  to  in  order  to  bring  moisture  to  the  surface  or 
upper  layer  of  soil.  Rolling  compacts  the  superficial  layer 
of  soil  and  thus  establishes  capillary  connection  with  the 
moist  soil  below.  This  may  be  desirable  in  order  to  bring 
moisture  in  contact  with  seeds,  but  although  germination 
is  hastened  loss  of  moisture  results. 

Subsurface  packing  is  designed  to  make  more  compact  a 
naturally  loose  soil  by  running  wedge-rimmed  wheels  through 
it.  If  the  soil  is  too  loose  for  capillary  movement  of  water 
to  proceed  effectively,  this  operation  promotes  it.  Its  use 
is  confined  to  arid  or  semi-arid  regions. 

94.  Removal  of  water  by  drainage.  —  Land  drainage  is 
any  condition,  natural  or  artificial,  that  enables  the  surplus 
water  to  escape  from  soils.  A  soil  may  be  highly  productive 
when  drained,  but  worthless  before  draining.  This  is  but 
another  illustration  of  the  many  factors  affecting  soil  pro- 
ductiveness. Where  natural  drainage  is  poor,  artificial 
drainage  is  general^  a  profitable  investment.  It  may  be 
accomplished  either  by  surface  ditches  or  by  underground 
drains. 

95.  Benefits  of  drainage.  —  There  are  many  ways  in 
which  good  drainage  benefits  soils  and  crops.  The  need  of 
drainage  may  be  very  evident  in  the  yellow  color  and  poor 
growth  of  young,  plants,  or  it  may  be  less  readily  detected,  and 
yet  may  be  sufficiently  needed  to  make  it  a  profitable  invest- 
ment. Good  drainage  is  the  first  requisite  in  enabling  a  soil 
to  reach  its  maximum  productiveness.  The  principal  ways 
in  which  drainage  benefits  the  soil  and  crop  are  as  follows : 


SOIL    WATER  79 

1.  Enlargement  in  the  supply  and  movement  of  soil  air. 

2.  Improvement  in  tilth. 

3.  More  available  water  throughout  the  growing  season. 

4.  Longer  growing  season. 

96.  Soil  air.  —  Drainage  increases  the  supply  and  move- 
ment of  soil  air  by  allowing  the  gravitational  water  to  run 
off  and  thus  to  be  replaced  by  air.  With  each  fall  of  rain 
there  is  a  movement  of  air  through  the  soil.  The  increased 
air  supply  is  of  benefit  in  the  following  ways : 

1.  It  furnishes  air  to  roots  which  require  it  for  the  proper 
performance  of  their  functions. 

2.  It  facilitates  the  decomposition  of  organic  matter  of 
all  kinds,  thus  disposing  of  the  vegetable  matter  incorporated 
with  the  soil,  and  permitting  the  most  beneficial  kind  of  de- 
composition (see  §§  59,  60). 

3.  It  furnishes  the  conditions  necessary  for  the  trans- 
formations of  nitrogen  in  the  soil  which  prepare  that  sub- 
stance to  be  used  by  plants  (see  §§  116-168). 

97.  Soil  tilth.  —  Alternate  drying  and  wetting  of  soil  is 
one  of  the  processes  that  causes  the  formation  of  granular 
structure  and  consequent  improvement  of  tilth.  A  soil 
that  is  constantly  saturated  or  very  wet  when  worked  in 
the  spring  assumes  a  compact  condition.  The  larger  air 
space  reduces  heaving  by  allowing  expansion  of  freezing 
water  within  the  soil,  and  diminishes  the  tendency  to  erosion, 
by  allowing  water  to  sink  quickly  into  the  soil,  instead  of 
running  over  the  surface. 

98.  Available  water  during  the  growing  season.  —  A  soil 
in  need  of  drainage  is  often  in  need  of  moisture  in  midsummer, 
because  when  it  does  dry  out  its  water-holding  capacity 
is  low,  on  account  of  its  compact  condition.  Furthermore, 
plants  form  shallow  roots  in  a  saturated  soil,  and  if  the 
weather  becomes  dry  later  in  the  season,  the  roots  do  not 
then  go  to  the  depth  necessary  to  reach  the  water  supply. 


80  SOILS   AND   FERTILIZERS 

It  frequently  happens,  therefore,  that  plants  suffer  much 
from  lack  of  moisture  on  a  soil  that  has  been  saturated  with 
water  during  the  early  part  of  the  growing  season. 

99.  Length  of  growing  season.  —  Drainage  increases 
the  length  of  the  growing  season  in  two  ways :  (1)  The  soil 
can  be  worked  much  earlier  than  on  poorly  drained  land. 
(2)  The  soil  becomes  warm  earlier,  because  it  is  easier  to  heat 
soil  particles  than  it  is  to  heat  water.  Then  too  the  evaporat- 
ing moisture  causes  a  lowering  of  the  soil  temperature. 
Seeds  germinate  more  quickly  and  uniformly  and  plants 
make  a  more  rapid  growth  on  account  of  the  warmer  soil. 

100.  Other  results  of  drainage.  —  All  of  these  improved 
conditions  unite  to  produce  larger  yields  of  crops  and  more 
uniform  growth.  Drainage  eliminates  the  continually 
wet  or  swampy  portions  of  fields  that  interfere  with  tillage 
operations  and  necessitate  working  the  field  in  sections. 
There  is,  accordingly,  an  economy  in  operation.  In  meadows 
and  pastures  the  kinds  of  forage  plants  that  grow  on  a  well- 
drained  soil  make  better  feed  than  those  kinds  that  grow 
on  wet  land. 

101.  Open  ditches.  —  Excess  water  is  sometimes  removed 
by  means  of  open  ditches  of  size  and  depth  necessary  to 
drain  water  from  the  land  and  carry  it  to  some  waterway. 
Such  ditches  sometimes  merely  follow  a  depression  or  swale 
in  the  land  and  thus  carry  off  the  worst  of  the  excess  water, 
especially  that  which  comes  from  higher  land,  or  they  are 
sometimes  laid  out  in  a  more  systematic  way. 

Level  fields  may  be  plowed  in  lands  with  dead  furrows 
every  twelve  to  twenty  feet  apart,  and  with  a  larger  ditch 
run  through  lower  ground  for  the  dead  furrows  to  empty 
into.  This  affords  only  surface  drainage,  but  is  better 
than  nothing.  Larger  ditches  should  have  grass  planted 
along  the  sides  for  several  feet  from  the  ditch.  Weeds  must 
be  mowed  and  trash,  dirt  and  stones  removed  at  intervals. 


SOIL    WATER  81 

Open  ditches  require  much  labor  to  keep  them  in  order, 
they  do  not  remove  the  water  so  thoroughly  as  do  tile  drains, 
and  they  not  only  occupy  a  considerable  area  but  they  inter- 
fere with  the  cultivation  of  much  land  on  account  of  the 
space  along  the  ditches  required  for  turning  the  teams  in 
cultural  operations.  Only  under  exceptional  conditions  may 
open  ditches  be  profitably  used  instead  of  tile  drains. 

102.  Tile  drains.  —  These  drains  are  composed  of  baked 
clay  or  hardened  concrete  cylinders  with  open  ends,  their 
length  being  about  one  foot  and  their  diameter  varying 
from  three  inches  to  eight  or  more.  These  tiles  are  laid 
end  to  end  on  the  bottom  of  ditches  two  to  four  feet  in  depth, 
having  a  fall  sufficient  to  carry  off  the  water  and  prevent 
the  tiles  from  becoming  clogged  with  soil  particles.  Tile 
should  not  be  made  of  clay  that  contains  particles  of  lime,  as 
the  lime  when  baked  is  converted  into  quicklime,  which 
causes  the  tile  to  crumble  when  buried  in  the  soil. 

It  is  not  necessary  that  tile  shall  be  permeable  to  water, 
as  it  is  through  the  openings  between  the  ends  of  the  tile 
that  water  enters,  and  not  through  the  pores.  Vitrified 
tile  may  well  be  used,  as  they  are  less  likely  to  be  injured 
by  freezing  than  are  porous  tile,  because  expansion  of  ab- 
sorbed water  on  freezing  causes  the  latter  to  disintegrate. 

Concrete  tile  are  often  used  and  these  may  be  made  on 
the  farm,  with  forms  constructed  for  the  purpose. 

Silt  and  fine  sand  may  enter  the  tiles  through  the  open- 
ings between  them,  and  to  guard  against  this  collars  are 
sometimes  placed  over  the  joints,  but  with  proper  grades 
this  is  not  necessary.  Sometimes  tile  are  hexagonal  on  the 
outside,  for  the  purpose  of  preventing  settling  of  the  tile 
in  places,  with  a  consequent  stoppage  with  silt.  However, 
if  the  bottom  of  the  ditch  is  carefully  made,  round  tile  are 
not  likely  to  deviate  from  alignment  and  they  are  more  easily 
laid. 


82 


SOILS   AND   FERTILIZERS 


103.  Arrangement  of  drains.  —  In  laying  out  a  system 
of  drains  certain  rules  must  be  regarded.  A  main  drain 
usually  follows  a  depression  in  the  land,  rising  with  the 

natural  grade,  or 
if  that  does  not 
give  a  sufficient 
rise,  becoming 
shallower  as  it 
ascends.  Some- 
times this  will  be 
sufficient  to  re- 
move the  surplus 
water,  but  more 
often  lateral 
drains  will  be  nec- 
essary. These  are 
of  smaller  tile  and 
are  usually  paral- 
lel to  each  other 
and  from  twenty 
to  a  hundred  feet 
apart.  This  ar- 
rangement is 
called  the  herring 
bone  system. 
(See  Fig.  15.) 
There  may  also  be 
submains  branch- 
ing off  of  the  main 
drain,  and  laterals 
running  into  the  submains.  This  is  known  as  the  gridiron 
system.  (See  Fig.  15.)  Sometimes  the  laterals  are  run 
across  the  slope,  but  usually  it  is  better  to  run  them  down. 
A  lateral  should  not  enter  a  main  drain  at  a  right  angle, 


Fig.  15.  —  The  upper  drawing  illustrates  the  her- 
ring bone  system  of  laying  tile  drains.  The  lower 
represents  the  gridiron  system. 


Plate  IX.  Drainage.  —  The  drain  outlet  is  often  poorly  constructed 
and  easily  clogged,  as  shown  in  the  upper  figure.  The  lower  one  is  well 
protected. 


SOIL    WATER  83 

but  an  acute  angle  should  be  formed  between  the  two  streams 
above  the  point  of  contact;  otherwise  the  flow  of  water 
will  be  impeded.  For  the  same  reason  two  laterals  should 
not  enter  a  main  drain  opposite  to  each  other. 

It  is  desirable  to  have  as  few  main  drain  outlets  as  possible, 
for  the  outlet  is  likely  to  be  the  weakest  point  in  a  drainage 
system.  If  it  becomes  clogged,  the  entire  system  is  put 
out  of  action.  It  is  more  likely  to  be  injured  by  freezing 
than  is  the  underground  tile,  and  unless  well  protected  it 
affords  an  opening  into  which  small  animals  may  crawl  and 
clog  the  system. 

The  quantity  of  water  removed  by  tiles  of  various  sizes, 
and  laid  at  certain  distances  and  grades  as  well  as  other 
operations  that  cannot  be  treated  here,  may  be  ascertained 
from  the  books  that  deal  exclusively  with  the  subject  of  land 
drainage. 

104.  Digging  ditches  and  laying  tile.  —  The  depth  of 
ditches  for  tile  drainage  varies  from  two  to  four  feet.  Three 
feet  is  the  usual  depth.  The  closer  together  the  laterals, 
the  shallower  the  drains  may  be  laid.  A  compact  soil, 
through  which  water  moves  very  slowly,  will  require  the 
use  of  shallow  drains.  A  lighter  soil  underlaid  by  hardpan 
will  also  require  shallow  drains.  The  shallower  the  drains 
in  any  soil,  the  closer  together  they  must  be  laid,  the  cus- 
tomary range  being  from  twenty  to  a  hundred  or  more  feet. 
Surplus  water  enters  the  drains  from  the  soil  immediately 
surrounding  them.  As  the  larger  pore  spaces  become 
partly  empty,  water  enters  them  from  surrounding  soil, 
and  in  this  way  drainage  gradually  extends.  The  soil  mid- 
way between  the  drains  is  the  last  to  lose  its  surplus  water, 
and  the  water  table  is  always  higher  between  drains  than 
over  them. 

The  distance  between  drains  must  be  small  enough  to 
allow  the  water  table  to  descend  promptly  to  a  point  where 


84 


SOILS  AND   FERTILIZERS 


it  will  not  interfere  with  root  growth.     The  more  permeable 
the  soil  and  the  deeper  the  drains,  the  further  apart  they  may 


<St/aFACE 


sS^/VDY      LO/1M 


Fig.  16.  —  Cross  sections  of  two  soils,  a  sandy  loam  and  a  clay,  both  of 
which  have  drain  tiles  laid  at  right  angles  to  the  sections.  Owing  to  the 
more  rapid  movement  of  water  through  the  sandy  loam,  the  tiles  are  laid 
twice  as  far  apart  as  they  are  in  the  clay.  They  are  also  deeper  in  the  former 
soil.  The  water  gradient  is  steeper  in  the  clay.  The  tiles  should  be  suf- 
ficiently close  together  to  keep  the  water  table  below  the  plowing  line. 

be  placed.     The  position  of  the  water  level  between  drains 
is  shown  in  Fig.  16. 

Ditches  may  be  dug  or  partly  dug  by  means  of  spades, 
ditching  plows  or  traction  ditchers.     The  last  named,  while 

Trie  Elements  or  Soil  Water  Control 


WATER  CONTROL. 


MOISTURE  CONSERVATION 


DRAINAGE 


WILTIN6  POINT. 


MAXIMUM  CAPILLARY 
CAPACITY 


3— H  OPTIMUM  50IL  MOISTURE*!— j 


UNAVAILABLE 
WATER 


AVAILABLE 
WATER 


!  5URPLU3 
WATER 


Fig.  17.  —  Diagrammatic  explanation  of  water  control  in  a  humid  region. 
On  the  one  hand  we  have  drainage  reducing  the  surplus  water  to  the  maxi- 
mum capillary  water  capacity  or  below  and  thus  bringing  it  within  the  range 
of  available  water.  On  the  other  we  have  moisture  conservation  by  means 
of  which  the  moisture  is  kept  above  the  content  of  unavailable  water  or  the 
wilting  point.  Somewhere  within  the  limits  of  available  water  lies  the 
optimum  moisture  content  for  plant  growth. 


SOIL    WATER  85 

expensive  in  first  cost,  is  economical  in  operation  in  many 
soils.  After  the  ditch  has  been  opened  to  its  full  depth, 
it  is  necessary  to  go  over  the  entire  bottom  to  remove  loose 
dirt  and  to  give  it  the  necessary  grade.  This  must  be  done 
by  hand.  Either  a  ditching  spade  or  a  drain  scoop  is  the 
best  implement  to  use.  A  fall  of  at  least  four  inches  in  a 
hundred  feet  is  necessary  under  most  conditions,  but  in 
clay  soils  less  fall  is  permissible,  as  there  is  less  danger  of 
silt  entering  the  drains. 

QUESTIONS 

1.  Name  the  three  forms  in  which  water  is  present  in  soils. 

2.  Explain  what   is    meant  by  hygroscopic  water.     Capillary 
water.     Gravitational  water. 

3.  On  what  does  the  content  of  hygroscopic  water  depend  ? 

4.  Name  six  conditions  that  tend  to  increase  the  capillary 
water  capacity  of  soil. 

5.  Explain  the  relation  of  soil   texture  to  the  movement  of 
capillary  water. 

6.  How  does  soil  texture   affect    the   rate    of   movement    of 
capillary  water  ? 

7.  What  are  the  conditions  that  affect  the  rate  of  flow  of  grav- 
itational water  ? 

8.  Explain  what  is  meant  by  the  water  table. 

9.  Describe  three  ways  in  which  water  contributes  directly  to 
plant  growth. 

10.  What  is  the  transpiration  ratio  ? 

11.  Name  three  factors  that  influence  it. 

12.  Calculate  the  number  of  inches  of  rainfall  transpired  by  a 
three-ton  crop  having  a  transpiration  ratio  of  250. 

13.  Name  four  ways  in  which  water  leaves  soil. 

14.  What  is  the  principle  of  the  soil  mulch  ? 

15.  State  four  ways  in  which  drainage  benefits  soils. 

LABORATORY   EXERCISES 

Exercise  I.  —  Determination  of  the  percentage  of  water  in  a  soil. 
Materials.  —  Samples  of  moist  soil,  torsion  balance,  evaporating 
dishes,  air  oven  and  flame,  desiccator.     See  Plate  IX. 


86  SOILS  AND   FERTILIZERS 

Procedure.  —  Carefully  obtain  the  weight  of  an  evaporating  dish 
on  the  balance.  Then  weigh  into  the  dish  50  grams  of  the  soil  to 
be  tested.  Air  dry  sample  in  laboratory  and  then  place  it  in  air 
oven  at  100°  C.  for  two  hours.  Cool  in  desiccator  and  weigh.  The 
loss  in  weight  is  water.  Calculate  the  percentage  of  moisture 
based  on  absolutely  dry  soil. 

Make  this  determination  in  duplicate  and  on  a  number  of  soils. 
Calculate  the  amount  of  water  in  an  acre  foot  of  the  various  soils, 
considering  them  to  weigh  3,500,000  pounds  per  acre  foot.  Note 
relation  of  soil  moisture  content  to  bare  and  cropped  soil,  kind  of 
crop,  stage  of  growth  and  previous  rainfall. 

Exercise  II.  —  Capillary  movement  in  different  soils. 

Materials.  —  Dry  samples  of  pulverized  sandy  loam,  silt  and 
clay,  three  long  glass  tubes  2  inches  in  diameter,  pans  for  water  and 
cheesecloth.     See  Plate  IX. 

Procedure.  —  Neatly  cover  the  ends  of  the  three  long  glass  cylin- 
ders by  tying  over  them  two  thicknesses  of  cheesecloth.  Fill  cylin- 
ders with  the  respective  soils  to  be  studied.  Be  sure  that  the 
compaction  is  uniform.  Now  set  the  ends  of  the  cylinders  in  water 
one  inch  deep  and  observe  the  height  of  capillary  movement  at  the 
following  periods  after  starting :  1  hour,  2  hours,  12  hours,  1  day, 
2  days,  3  days,  4  days,  etc.  Continue  experiment  as  long  as  prac- 
ticable. Tabulate  data  and  draw  curves.  Explain  the  practical 
importance  of  the  results  obtained. 

Exercise  III.  —  Rate  of  percolation  of  water  through  soils. 

Materials.  —  Dry,  well-pulverized  sand  and  clay  loam,  two  lamp 
chimneys,  cheesecloth,  torsion  balance.     See  Exercise  V,  Chapter  V. 

Procedure.  —  Prepare  two  lamp  chimneys  by  neatly  tying  two 
thicknesses  of  cheesecloth  over  their  bottoms.  Place  in  one  a 
definite  and  known  amount  of  sand.  In  the  other  place  the  same 
weight  of  clay  loam.  Give  each  a  uniform  compaction.  Now  weigh 
each  chimney  with  its  content  of  soil. 

Place  the  chimneys  in  such  a  position  as  to  allow  free  drainage 
and  add  the  same  amount  of  water  to  each,  keeping  the  head  of  water 
constant  in  each  chimney.  Observe  the  rate  of  the  downward 
movement  of  water  through  the  two  soils.  When  percolation  has 
begun,  measure  percolate  for  15  minutes  and  express  rate  in  cubic 
centimeters  per  hour. 

Explain  the  reasons  for  the  results  obtained  and  the  practical 
importance  thereof. 


J  l    !  f1 

•  *  H  J  i- 

1     - 

—              ■•       rirmnr  * 

s  ° 

•2  b 


53  & 

en   O 

=3    _ 


go 
«  a 
«.2 
o  g 

02     GO 

bfi  S 

o  .3 


H 

* 

* 

O, 

W 

a 

1 

C3 

a 

M 
P 

X 

3 

03 

o 

w 

s 

o 

a 

a 

p 

o 

g 

O 

a 

fcJD 

M 

O 

h 

SS 

02 

5 

8 

H 

a 

* 

M 

s 

<1 

E 

Oh 

3 

Pk 

^ 

Q 

H 

c 

! 

1 

EH 

< 

d 
o 
'■{3 

C 

| 

s 

s  £ 

SOIL    WATER 


87 


Exercise  IV.  —  Water-holding  capacity  of  soils. 

Materials.  —  Same  as  in  Exercise  III. 

Procedure.  —  When  Exercise  III  is  complete,  cover  chimneys  and 
allow  all  the  free  water  to  drain  away.  Then  weigh  the  chimneys 
and  wet  soil.  The  increased  weight  is  water  retained.  Calculate 
the  percentage  of  water  retained  by  each  soil  based  on  the  weight 
of  the  original  sample. 

Write  out  a  full  description  of  the  experiment  and  the  points 
of  importance  that  it  shows. 

Exercise  V.  —  Moisture  conservation  by  means  of  a  soil  mulch. 

Materials.  —  Three  tumblers,  one  of  which  should  be  one  inch 
shorter  than  the  other  two,  moist  soil,  dry  clay  loam  and  dry  sand, 
torsion  balance. 

Procedure.  —  Fill  the  short  tumbler  level  full  with  a  well-mixed 
moist  soil.     This  is  to  serve  as  the  unmulched  treatment.     Place 


CLAY  LOAM  MULCH 


5ANDY  LOAM  MULCH 


NO    MULCH 

I 


MOI5T50IL 


MOIbT  SOIL 


riOI6T50IL 


Fig.  18.  —  Tumblers  filled  with  equal  quantities  of  a  moist  soil  and  pre- 
pared for  a  demonstration  of  the  effectiveness  of  mulches  in  the  conserva- 
tion of  moisture.  Losses  of  moisture  by  evaporation  are  measured  by  weigh- 
ing the  tumblers. 

exactly  the  same  amount  of  moist  soil  in  each  of  the  other  tumblers 
as  is  used  in  the  shorter  one,  compacting  to  within  one  inch  of  the  top. 
On  the  surface  of  one  place  one  inch  of  dry  clay  loam  and  on  the 
other  one  inch  of  dry  sand.     Weigh  the  tumblers  now  fully  prepared. 

Set  tumblers  in  a  place  of  uniform  temperature  and  weigh  daily 
for  a  week.  The  loss  of  weight  each  day  is  moisture.  Tabulate 
data  and  draw  curves. 

Explain  the  significance  of  the  results  obtained. 


88 


SOILS   AND   FERTILIZERS 


Exercise  VI.  —  Loss  of  water  by  transpiration. 

Materials.  —  Glazed  gallon  butter  jar,  oats  seed,  paraffined  paper, 
thistle  tube,  coarse  sand  and  heavy  balance. 

Procedure.  —  Fill  a  glazed  jar  with  rich  soil,  first  adjusting  coarse 

sand  and  thistle  tube  as  shown  in 
Fig.  19.  Moisten  soil  with  water, 
but  not  too  wet,  and  plant  with  oat 
seed.  When  seedlings  are  one  week 
old,  thin  to  suitable  number.  Then 
cover  surface  of  soil  with  paraffined 
paper,  allowing  plants  to  protrude 
through  small  holes  cut  for  that  pur- 
pose. Paraffine  the  paper  to  side  of 
jar  so  that  all  losses  of  moisture  by 
evaporation  may  be  prevented. 
Bring  soil  up  to  optimum  water  con- 
tent and  weigh.  You  are  now  ready 
to  record  losses  by  transpiration. 

Weigh  jar  each  week,  replacing 
water  lost  through  the  thistle  tube. 
Record  data  and  draw  curves.  By 
changing  the  jar  from  sunshine  to 
shade,  warm  temperature  to  cold, 
high  humidity  to  low,  etc.,  the  fac- 
tors influencing  transpiration  may 
be  studied. 

Jars  with  different  crops,  different  soil  or  the  same  soil  with  differ- 
ent fertilizers  or  different  water  treatments  may  be  utilized  if  so 

desired. 

r 

Exercise  VII.  —  Review  problems.     Chapters  IV  and  VI. 

1.  A  soil  weighs  100  lbs.  per  cubic  foot  when  dry.  The  weight 
of  a  cubic  foot  of  water  is  62.5  lbs.  Calculate  its  apparent  specific 
gravity  and  weight  per  acre  foot.  Ans.   1 .6  and  4,356,000  lbs. 

2.  This  soil  has  an  absolute  specific  gravity  of  2.7.  Calculate 
its  pore  space. 

%  pore  space  =100 


Fig.  19.  —  Glazed  jar  equipped 
for  observation  of  transpiration 
of  water  from  plants,  (a)  thistle 
tube  for  watering,  (6)  plants,  (c) 
paraffined  paper  to  prevent  evap- 
oration from  the  soil  surface,  (d) 
soil,  (e)  gravel. 


Tap,  sp.  gr.  x  10Q-I 
Labs.  sp.  gr.       1  J 


Ans.  40.7+%. 


3.    This  soil  contains  10  pounds  of  water  a  cubic  foot.     Calculate 
percentage  of  water  based  on  absolutely  dry  soil.     On  wet  soil. 

Ans.   10%  and  9.09%. 


SOIL    WATER  89 

4.  By  the  following  formula,  calculate  the  air  space  present. 

%  air  space  =  %  pore  space  -  (%  water  X  ap.  sp.  gr.)    'Ans.  24.7  %. 

5.  The  wilting  point  in  this  soil  is  4  percent.  What  is  the  per- 
centage of  available  water  ?  Weight  of  available  water  per  cubic 
foot  ?    Per  acre  foot  ?  Arts.  6  %,  6  lbs.  and  261,360  lbs. 

Exercise  VIII.  —  Tile  drainage. 

If  possible,  have  the  class  install  a  short  drainage  system.  They 
should  dig  at  least  part  of  the  ditch,  grade  the  bottom,  lay  the  tile 
and  build  the  outlet.  The  explanation  of  every  point  involved  as 
the  work  proceeds  will  give  such  an  exercise  great  practical  value. 
It  will  also  make  the  classroom  work  much  more  effective. 

If  drainage  operations  are  being  conducted  in  the  near  vicinity, 
the  class  should  by  all  means  bp  taken  to  inspect  them.  The 
general  plan  of  the  work,  as  well  aJs  the  more  detailed  phases,  should 
be  explained  by  the  teacher.  Materials  and  illustrations  may  also 
be  obtained  for  later  discussion  and  study  in  the  classroom.  If 
ditching  machinery  is  being  utilized,  it  also  should  be  given  consider- 
able study. 

Early  in  the  spring,  while  the  soil  is  still  wet,  a  field  trip  might 
well  be  taken.  The  need  of  drainage,  the  movement  of  water 
through  soil,  the  effectiveness  of  drainage,  the  entraiice  of  water  into 
a  drainage  system,  the  movement  of  water  through  tile,  good  and 
poor  outlets  and  the  drainage  of  roads  could  be  studied  with  profit. 


CHAPTER  VII 
PLANT-FOOD  MATERIALS  IN  SOILS 

Plants  secure  their  mineral  food  materials  exclusively 
from  the  soil.  In  a  state  of  nature  plants  at  death  fall 
on  the  surface  of  the  ground  and  as  decay  proceeds,  their 
ash  constituents  return  to  the  soil.  The  loss  of  mineral 
matter,  under  these  conditions,  is  due  almost  entirely  to 
its  solution  and  removal  in  drainage  water,  or  to  erosion. 
Under  ordinary  farm  practice  the  procedure  is  different. 
The  aboveground  portions  of  plants  are  removed  wholly, 
or  in  part,  from  the  land  and  the  loss  of  easily  soluble  min- 
eral matter  is  thus  greatly  increased.  The  soil  supply  of 
those  particular  elements  required  for  the  growth  of  crops 
is  a  matter  of  great  importance,  for  it  is  upon  this  that  man 
must  depend  for  his  sustenance,  and  although  he  may 
supplement  these  elements  in  the  soil  by  the  use  of  manures, 
the  cost  of  food  is  thereby  materially  increased. 

105.  Variations  in  content  of  plant  nutrients  in  different 
soils.  —  There  are  wide  differences  in  the  quantities  of  plant- 
food  materials  in  soils  from  different  localities,  although 
the  localities  may  be  near  together.  This  is  illustrated  by 
the  following  statement  of  the  analyses  of  soils  from  different 
parts  of  the  country,  the  number  of  pounds  of  each  ingredi- 
ent being  based  on  the  weight  of  2,000,000  pounds  of  soil, 
which  is  about  the  weight  of  the  furrow  slice  of  an  acre  of 
land. 

90 


PLANT-FOOD   MATERIALS  IN  SOILS 


91 


Table  17.  —  Composition  of  Some  Arable  Soils  Based  on 
Ultimate  Analyses 


Pounds  in  2,000,000  Lbs. 

op  Soil 

Percentage  Composition 

Location 

Nitro- 
gen 

Phos- 
phoric 
Acid 

Potash 

Lime 

Nitro- 
gen 

Phos- 
phoric 
Acid 

Potash 

Lime 

New  York 

2,520 

1,680 

40,200 

6,600 

0.126 

0.084 

2.010 

0.330 

New  York 

2,860 

1,620 

33,400 

4,600 

0.143 

0.081 

1.670 

0.230 

New  York 

2,800 

3,280 

17,200 

68,400 

0.140 

0.164 

0.860 

3.420 

New  York 

4,000 

3,920 

39,200 

5,400 

0.200 

0.196 

1.960 

0.270 

Ohio  »  .     . 

1,260 

966 

43,975 

11,303 

0.063 

0.043 

2.198 

0.565 

Ohio1.     . 

3,844 

14,008 

67,285 

78,772 

0.192 

0.700 

3.364 

3.938 

Ohio  »  .     . 

186 

3,106 

37,214 

15,478 

0.009 

0.155 

1.860 

0.773 

Ohio  i  .     . 

2,974 

1,580 

37,070 

4,480 

0.148 

0.079 

1.853 

0.224 

Illinois2   . 

6,480 

4,145 

42,493 

28,644 

0.324 

0.207 

2.124 

1.432 

Illinois  8   . 

6,020 

3,710 

39,165 

104,636 

0.301 

0.185 

1.958 

5.232 

The  soils  whose  analyses  are  stated  in  the  table  given  above 
are  all  from  arable  land  and  while  they  represent  wide  differ- 
ences in  some  of  their  constituents  none  of  them  is  so  deficient 
in  any  plant  nutrient  as  to  prevent  it  from  producing  crops. 
Comparing  the  quantities  of  the  constituents  of  these  soils,  we 
find  that  in  the  Illinois  soils  the  lime  varies  from  28,644 
pounds  to  104,636  pounds  in  2,000,000  pounds  of  soil.  In  Ohio 
the  same  constituent  ranges  from  4480  to  78,772  pounds 
with  nearly  as  low  a  minimum  in  New  York.  The  nitrogen 
in  Ohio  rises  from  a  minimum  of  186  pounds  to  a  maximum  of 
3844  pounds  while  the  maximum  for  Illinois  is  6480  pounds. 
The  greatest  range  of  phosphoric  acid  is  from  966  pounds  to 
14,008  pounds,  both  of  which  soils  occur  in  the  same  state. 

Another  fact  brought  out  by  this  table  is  that  a  soil  may 
be  rich  in  one  ingredient  and  poor  in  another,  also  that  soils 
lying  near  together  may  differ  more  in  composition  than  do 
soils  that  are  widely  separated. 


1  Ohio  Experiment  Station  Bui.  261. 
» Illinois  Soil  Report  No.  10. 


» Illinois  Soil  Report  No.  2. 


92 


SOILS   AND   FERTILIZERS 


106.  The  total  supply  of  plant-food  materials.  —  The 
statement  of  analyses  in  Table  17  shows  the  quantities  of 
plant  nutrients  in  2,000,000  pounds,  which  represents  the 
weight  of  an  acre  of  soil  to  a  depth  of  only  six  to  eight  inches. 
There  is  below  this  a  considerable  volume  of  soil  through 
which  roots  ramify,  and  from  which  some  nutriment  is 
drawn.  The  roots  of  ordinary  crops  extend  to  a  depth  of 
three  or  four  feet  into  the  soil,  depending  on  different  condi- 
tions of  soil  and  climate.  In  semi-arid  and  arid  regions 
roots  extend  deeper  than  they  do  in  humid  regions,  and  in 
well-drained  soils  they  penetrate  deeper  than  they  do  in 
poorly  drained  ones.  It  is,  however,  from  the  furrow  slice 
that  plants  derive  most  of  their  nourishment. 

Subsoils  sometimes  contain  more  and  sometimes  less 
plant-food  materials  than  do  the  surface  soils.  Nitrogen 
is  almost  always  present  in  greater  quantity  in  the  surface 
soil,  because  it  is  a  constituent  of  material  that  has  been 
plowed  into  the  furrow  slice.  Table  18  contains  a  statement 
of  the  analyses,  expressed  in  percentage  composition,  of  two 
soils  to  a  depth  of  four  feet,  each  foot  of  which  was  analyzed 
separately. 

Table  18.  —  Ultimate  Analyses  of  Two  Soils  to  a  Depth  of 
Four  Feet,  Expressed  in  Percentage  Composition 


Dunkirk  Clay  Loam 

Volusia  Silt  Loam 

1st  ft. 

2nd  ft. 

3rd  ft. 

4th  ft. 

1st  ft. 

2nd  ft. 

3rd  ft. 

4th  ft. 

Nitrogen  .     . 

.126 

.067 

.064 

.064 

.143 

.052 

.059 

.050 

Phosphoric 

acid       .     . 

.084 

.066 

.103 

.125 

.081 

.039 

.018 

.071 

Lime     .     .     . 

.330 

.270 

.520 

1.780 

.230 

.160 

.260 

.360 

Magnesia 

.160 

.150 

.150 

.320 

.560 

.390 

.290 

.400 

Potash      .     . 

2.010 

2.480 

2.550 

2.630 

1.670 

1.790 

2.000 

2.140 

Plate  XI.  Surface  Soil  and  Subsoil.  —  Note  the  difference 
between  the  top  soil  and  the  subsoil  in  the  upper  figure  ;  also  the  abun- 
dant growth  of  plant  roots  in  the  top  soil  as  compared  with  the  subsoil  in 
the  lower  figure. 


PLANT-FOOD   MATERIALS   IN  SOILS  93 

These  analyses  show  in  some  cases  more,  and  in  others 
less,  of  the  various  constituents  below  the  surface  foot, 
with  the  exception  of  nitrogen,  which  is  always  less  in  the 
subsoil.  The  fact  that  the  greater  part  of  the  roots  of 
most  plants  is  in  the  surface  soil  makes  the  draft  greater 
on  that  layer,  but  the  total  volume  to  a  depth  of  four  feet, 
or  even  more,  may  be  considered  to  be  the  feeding  ground 
of  crops. 

107.  Upward  movement  of  plant-food  materials.  —  There 
is  another  way  in  which  the  soil  to  a  considerable  depth 
may  contribute  to  the  nourishment  of  crops.  This  is  by 
furnishing  plant-food  materials  that  are  carried  upward 
by  ascending  currents  of  moisture,  or  that  are  absorbed  by 
roots  from  the  lower  depths  and  deposited  near  the  surface 
when  the  plants  die.  To  what  extent  the  upward  movement 
due  to  moisture  is  operative  is  something  of  a  question ; 
in  humid  regions  probably  very  slightly,  in  semi-arid  and 
arid  regions  it  is  doubtless  of  considerable  moment,  as  indi- 
cated by  the  existence  of  alkali  crusts. 

108.  Plant  nutrients  compose  a  small  part  of  the  soil.  — 
Another  point  brought  out  by.  Table  17  is  the  very  small 
proportion  of  the  soil  that  is  represented  by  plant-food  ma- 
terials. For  instance,  the  sum  of  all  of  the  nitrogen,  phos- 
phoric acid,  lime,  magnesia  and  potash  is  not  much  more 
than  two  percent  of  the  total  weight  of  the  soil,  and  it  would 
be  easy  to  find  analyses  that  would  show  much  less.  Some 
of  the  very  important  substances  are  present  only  in  tenths 
or  even  hundredths  of  a  percent.  The  great  bulk  of  the 
soil  contributes  nothing  to  plant  growth  other  than  to  furnish 
mechanical  support  and  to  store  air  and  water  for  the  use 
of  roots. 

109.  Relation  of  composition  to  productiveness.  —  The 
productiveness  of  a  soil  is  not  necessarily  directly  propor- 
tional to  the  quantity  of  plant-food  materials  that  it  con- 


94 


SOILS   AND   FERTILIZERS 


tains.  This  is  because  there  are  so  many  conditions,  to 
which  soils  are  subject,  that  interfere  with  the  ability  of 
plants  to  obtain  the  nutrients  or  that,  in  other  ways,  inter- 
fere with  plant  growth.  It  is,  however,  possible  for  the 
quantity  of  some  substance  required  by  plants  to  be  so  small 
that  it  is  not  sufficient  to  furnish  enough  nutriment  for  prof- 
itable crop  production.     Probably  all  of  the  soils,  whose 


Fig.  20.  —  Relative  quantities  of  potash,  lime,  phosphoric  acid  and  nitro- 
gen in  a  sack  containing  200  pounds  of  dry  soil,  when  the  percentages  present 
are  respectively  1.98,  1.64,  0.19  and  0.165. 

analysis  is  stated  in  Table  17,  would  be  benefited  by  the 
application  of  some  fertilizers,  with  the  possible  exception 
of  the  rich  prairie  soils.  This  is  not  because  there  is  not 
actually  enough  plant-food  material  in  the  soil,  but  because 
it  is  not  in  a  form  that  is  available  to  plants. 

110.  Available  and  unavailable  plant-food  materials.  — 
The  available  plant-food  materials  in  soils  consist  of  those 
portions  of  the  total  supply  that  plants  are  able  to  secure 
in  their  growth.     We  have  seen  that  it  is  necessary  for  all 


PLANT-FOOD    MATERIALS   IN   SOILS  95 

substances  to  be  in  solution  in  order  that  they  shall  be 
absorbed  by  plants.  Soil  is  not  readily  soluble.  The  natu- 
ral insolubility  of  soil  is  modified  by  various  conditions 
of  the  soil  itself  and  by  the  plants  that  grow  on  it.  The  rate 
of  availability  of  plant  nutrients  is,  therefore,  not  a  constant 
quantity  for  any  soil.  A  soil  in  good  tilth  will  produce  much 
better  crops  than  a  soil  in  poor  tilth,  which  means  that  the 
rate  of  availability  of  its  plant  nutrients  changes  with 
the  physical  condition  of  the  soil. 

The  available  plant-food  materials  are  not  necessarily 
proportional  to  the  quantities  of  plant-food  materials  in  a 
soil.  One  piece  of  land  may  contain  more  plant  nutrients 
than  another  and  yet  be  less  productive.  It  has  been  shown 
that  the  addition  of  four  or  five  volumes  of  quartz  sand  to 
one  volume  of  a  heavy,  but  highly  productive,  black  clay  soil 
greatly  increased  the  productiveness,  although  the  conse- 
quent dilution  of  plant-food  content  reduced  the  potash  to 
0.12  percent  and  the  phosphoric  acid  to  0.03  percent.  The 
mechanical  condition  of  the  soil  was  better  after  applying 
the  sand. 

111.  Conditions  that  influence  availability.  —  It  is  appar- 
ent that  the  immediate  availability  of  the  plant-food  materials 
in  a  soil  is  not  so  much  a  matter  of  their  total  quantity,  as 
of  favorable  conditions  for  the  decomposition  of  both  the 
organic  and  the  inorganic  matter  in  the  soil,  and  for  the  growth 
of  plants.  For  this  reason  good  tilth,  good  drainage,  warmth, 
absence  of  acidity  and  the  kind  and  vigor  of  the  plants  are 
factors  that  influence  availability.  When  any  one  or  more 
of  these  conditions  is  unfavorable,  the  availability  of  the 
plant  nutrients  may  be  decreased. 

While  all  of  these  conditions  influence  the  availability 
of  the  plant-food  materials,  it  still  remains  true  that,  other 
things  being  equal,  the  greater  the  total  supply  of  each  of 
these  constituents  of  a  soil,  the  greater  will  be  the  total 


96  SOILS   AND    FERTILIZERS 

quantity  of  available  plant  nutrients,  and  the  greater  the 
productiveness  of  the  soil  is  likely  to  be.  Hence,  it  is 
desirable  to  conserve  the  supplies  of  these  substances 
and  to  augment  them,  if  possible,  by  their  judicious  ap- 
plication in  the  form  of  farm  manures  and  other  fertilizing 
materials,  and  especially  to  maintain  the  store  of  organic 
matter. 

112.  Water-soluble  matter  in  soil.  —  Although  soil  is 
very  slightly  soluble  in  water,  an  extract  of  soil  made  with 
water  contains  all  of  the  substances  required  by  plants. 
The  solution  obtained  by  extracting  a  soil  with  water  is 
probably  not  identical  in  composition  or  concentration  with 
the  solution  presented  to  the  root-hairs  of  plants  for  their 
nourishment,  because  the  plant  by  the  excretion  of  carbon 
dioxide,  and  possibly  in  other  ways,  aids  in  dissolving  plant 
nutrients.  It  is  probably  true,  however,  that  the  solution 
obtained  by  water  is  the  nearest  approximation  that  we  have 
to  the  solution  presented  to  roots  and  is,  for  that  reason, 
deserving  of  attention. 

113.  Relation  of  water-soluble  matter  to  productiveness. 
—  It  might  be  expected  that  there  would  be  a  direct  relation 
between  the  productive  capacity  of  a  soil  and  the  quantities 
of  plant  nutrients  in  its  water  extract,  and  that  this  relation 
would  hold  between  different  soils.  This  would  imply  that, 
as  between  two  or  more  soils;  the  plant-food  materials  dis- 
solved by  water  would,  in  general,  be  proportional  to  the 
quantities  of  the  readily  available  constituents  in  the  soil. 
It  has  been  demonstrated  that  such  relations  do  obtain 
between  certain  soils,  but  it  has  not  been  proven  that  this 
is  invariably  the  case.  Indeed  it  is  probable  that  soils  which 
differ  little  in  their  productivity  would  not,  in  every  instance, 
show  such  a  direct  proportional  relationship.  Experiments 
with  four  good  and  four  poor  soils  showed  the  following 
averages  for  their  crop  yields  and  water  extracts. 


PLANT-FOOD   MATERIALS  IN  SOILS 


97 


Table  19.  —  Average  Yields  and  Composition  of  Water  Ex- 
tracts of  Four  Good  and  Four  Poor  Soils 


Crop  Yields  per  Acre 

Corn,  bushels 

Potatoes,  bushels 

Water  soluble  salts  in  pounds  per  acre  of  surface 
four  feet 

Nitrogen 

Phosphoric  acid 

Potash 

Lime 

Magnesia 


Good  Soils 


64.3 
213.2 


82 

192 

319 

1422 

576 


A  somewhat  similar  result  was  obtained  with  two  soils 
contained  in  large  tanks  from  which  drainage  water  was 
collected,  and  that  have  been  under  experiment  for  a  num- 
ber of  years.  Each  tank  holds  about  three  and  one-half 
tons  of  soil.  In  1915  tanks  filled  with  soils  of  different  types 
were  planted  to  corn.  The  yields  of  grain  and  stalks  com- 
bined are  given  in  Table  20  and  also  the  number  of  pounds 
to  the  acre  of  plant  nutrients  in  drainage  water  collected 
during  seven  months  from  the  same  soil  types  kept  bare 
of  vegetation.  As  only  a  trace  of  phosphoric  acid  was  found 
in  the  drainage  that  ingredient  is  not  included  in  the  table. 

Table  20.  —  Yields  of  Crop  and  Plant-Food  Material  in 
Drainage  Water  from  Two  Soil  Types 


Soil  Type 

Dunkirk 
Clay  Loam 

Volusia 
Silt  Loam 

Yield  of  corn  silage  (tons  per  acre)       .... 
Substances  in  drainage  water  (lbs.  per  acre) 

Nitrogen 

Lime   .          

13.4 

72 
438 

81 
100 

7.8 

59 
360 

Magnesia 

57 

Potash 

52 

98  SOILS   AND   FERTILIZERS 

In  this  case,  as  in  that  of  the  four  soils,  previously  cited, 
there  is  a  correlation  between  the  productiveness  of  the  soils 
and  the  composition  of  the  water  extract. 

114.  Chemical  analysis  of  soil.  —  There  have  been  many 
methods  devised  for  the  chemical  analysis  of  soil.  The 
important  difference  between  these  is  in  the  solvent  used 
to  bring  the  soil  into  solution.  Most  solvents  dissolve  only 
a  part  of  the  soil,  in  which  case  the  result  of  the  analysis 
does  not  show  the  entire  amount  of  all  the  constituents,  and 
does  not,  therefore,  show  the  total  quantity  of  the  plant-food 
materials  in  the  soils.  The  figures  given  in  Table  17  are 
obtained  from  a  complete  solution  of  the  soils  analyzed  and 
hence  show  their  ultimate  composition. 

The  advantage  of  an  analysis  of  this  kind  is  that  one  can 
judge  of  the  lasting  qualities  of  the  soil,  and  if  any  particular 
constituent  is  present  in  very  minute  quantity  that  fact 
is  disclosed,  and  measures  can  be  taken  to  augment  the 
supply,  but  nothing,  however,  as  to  immediate  productive- 
ness can  be  learned.  A  collection  of  rocks  may  yield  to  this 
analysis  as  much  phosphoric  acid,  potash,  lime,  or  other 
nutrient,  as  a  rich  soil.  Such  an  analysis  is  useful  only  to 
ascertain  the  ultimate  limitations  of  a  soil,  or  its  possible 
deficiency  in  any  essential  constituent. 

Various  solvents  have  been  used  with  the  intention  of 
finding  the  quantities  of  food  materials  that  plants  may  be 
expected  to  obtain  in  a  reasonable  length  of  time,  or  in  other 
words  to  determine  the  available  plant-food  materials. 
These  methods  fail  because  availability,  as  we  have  just 
seen,  depends  on  the  conditions  to  which  a  soil  is  subjected 
in  the  field,  and  as  these  naturally  var}'  from  time  to  time 
it  is  impossible  to  find  any  one  solvent  that  will  measure 
such  a  variable  quantity  as  availabilitj^. 

Chemical  analyses  of  soil  are  useful  in  connection  with 
investigations  of  questions  relating  to  soils  but  it  is  not 


PLANT-FOOD   MATERIALS   IN  SOILS 


99 


always  possible,  as  the  result  of  a  chemical  analysis,  to  esti- 
mate the  -degree  of  productiveness  of  a  soil,  or  to  say  that  it 
should  have  a  certain  kind  of  fertilizer  treatment,  or  that  it 
is  adapted  to  certain  crops. 

115.  Absorptive  properties  of  soils.  —  If  a  solution  of 
certain  substances  required  by  plants  be  poured  on  soil  they 
will  not  leach  through  the  soil  unaltered,  but  part  will  be 
held  by  the  soil.  On  the  other  hand,  the  drainage  water 
may  contain  an  increased  quantity  of  some  other  substance 
in  place  of  the  one  added  in  solution.  As  an  example  of 
this  we  may  take  the  following  case.  An  application  of 
200  pounds  to  the  acre  of  a  potash  fertilizer  was  made 
annually  for  five  years  to  soil  contained  in  one  of  the  large 
tanks  previously  referred  to.  The  composition  of  the  drain- 
age water  from  the  tank  so  treated,  and  of  the  drainage 
water  from  an  untreated  soil  is  shown  in  the  following  table  : 

Table  21.  —  Annual  Average  Pounds  to  the  Acre  of  Lime, 
Magnesia  and  Potash  in  Drainage  from  Soil  Treated 
with  Potash  Fertilizer  and  from  Untreated  Soil 


Constituents  in  Drainage  Water 

Lime 

Magnesia 

Potash 

Potash  fertilizer      .... 
No  fertilizer        

298 

248 

81 
56 

53 
55 

In  this  case  the  effect  of  the  application  of  the  potash 
fertilizer  was  to  increase  the  quantities  of  lime  and  magnesia 
in  the  drainage  water,  but  not  the  quantity  of  potash.    . 

116.  Selective  absorption.  —  Some  substances  are  retained 
by  soils  only  in  small  part.  Among  these  are  nitrates, 
which,  as  we  shall  see  later,  are  very  important  forms  of 
nitrogen,  and  sulfates,  which  are  also  required  by  plants 


100  SOILS   AND   FERTILIZERS 

When  sulfate  was  added  annually  to  soil  in  one  of  the  tanks 
already  mentioned,  for  a  period  of  five  years,  as  much  as 
two-thirds  of  the  quantity  applied  was  removed  in  the  drain- 
age water,  in  addition  to  what  would  have  been  removed  if 
the  soil  had  received  no  sulfate.  The  potash  previously 
mentioned  as  having  been  applied  to  this  soil,  and  the  sulfate 
here  spoken  of  were  one  substance  called  sulfate  of  potash. 
The  latter  was  held  by  the  soil  and  the  sulfate  largely  leached 
through.  It  is  evident  that  the  substance  was  decomposed 
in  part  or  in  whole. 

It  is  thus  apparent  that  there  are  certain  soluble  fertilizers 
that  may  be  applied  to  soils  without  much  danger  of  loss 
by  leaching  and  other  fertilizers  that  are  likely  to  be  partly 
carried  out  of  the  soil  in  this  way. 

117.  The  availability  of  absorbed  fertilizers.  —  When  a 
soluble  fertilizer  is  absorbed  by  a  soil,  a  part  of  it,  at  least, 
is  held  in  a  condition  in  which  it  is  more  readily  available 
to  plants  than  is  the  large  mass  of  plant-food  material  origi- 
nally in  the  soil.  Thus  there  may  be  in  a  soil  several 
thousand  pounds  to  an  acre  of  nitrogen,  phosphoric  acid  or 
potash  in  the  three  or  four  feet  through  which  roots  ramify, 
and  yet  the  yield  of  crops  on  this  soil  may  be  materially 
increased  by  the  application  of  less  than  a  hundred  pounds 
of  one  or  more  of  these  substances. 

The  ability  of  soil  to  hold  fertilizers  in  a  readily  available 
form  is  strikingly  illustrated  by  an  experiment  at  the  Rotham- 
sted  Experiment  Station  in  which  soil  from  plats  that  had 
been  treated  with  certain  fertilizers  for  many  years  was 
thoroughly  extracted  with  water  and  the  extracts  analyzed. 
Complete  analyses  of  the  soil  from  the  several  plats  were 
also  made.  The  yields  of  crops  on  these  plats  had  been 
recorded  for  many  years  and  the  annual  average  of  these, 
together  with  the  analytical  data,  is  given  in  the  accompany- 
ing table : 


PLANT-FOOD   MATERIALS   iW  SOILS, 


101 


Table  22. 


Yields  of  Crops  and  Composition  of  Soil  and 
Water  Extract  of  Soil 


Yield 
per 

Acre 

Pounds 

Complete  Analy- 
sis Percentages 

Water  Extract 
Parts  per  Million 

Soil  Treatment 

Phos- 
phoric 
acid 

Potash 

Phos- 
phoric 
acid 

Potash 

Unmanured 

Nitrogen  and  phosphoric 

acid 

Nitrogen  and  potash    .     . 
Complete  fertilizer .     .     . 
Farm  manure      .... 

1,276 

3,972 

2,985 
5,087 
6,184 

0.099 

0.173 
0.102 
0.182 
0.176 

0.183 

0.248 
0.257 
0.326 
0.167 

0.525 

3.900 
0.808 
4.025 
4.463 

3.40 

3.88 
30.33 
24.03 
26.45 

It  may  be  observed  that  the  water  extract  of  the  soil  from 
the  plats  treated  with  any  fertilizer  ingredient  was  much 
richer  in  that  constituent  than  were  the  plats  not  so  treated, 
while  the  total  quantities  found  in  the  soil  were  not  propor- 
tionately increased. 

118.  Other  forms  of  available  plant-food  materials  in  soil. 
—  The  natural  weathering  of  soil  that  goes  on  continually 
makes  soluble  a  part  of  the  originally  insoluble  mineral  mat- 
ter and  this  is  absorbed  just  as  are  the  fertilizer  salts.  When 
land  is  cropped  each  year,  this  soluble  matter  is  used  by 
plants  about  as  quickly  as  it  is  formed,  but  when  land  is 
bare  fallowed  the  dissolved  matter  is  largely  absorbed,  and 
thus  a  bare  fallow  increases  the  quantity  of  available  nutri- 
ents for  the  following  crop. 

Another,  and  very  important  supply  of  available  plant 
nutrients,  is  that  combined  with  the  organic  matter  in  soils. 
When  organic  matter  is  incorporated  with  soil,  decomposi- 
tion begins,  acids  are  formed  and  these  unite  with  mineral 
matter  previously  in  a  difficultly  soluble  condition.  The 
result  is  a  compound,  partly  organic  and  partly  inorganic. 
These  compounds  decay  still  further  until  all  the  organic 
matter  passes  off  as  we  have  already  seen  (§  50),  and  the 


102 


SOILS    AND   FERTILIZERS 


inorganic  matter  that  remains  is  either  used  directly  by  plants 
or  is  absorbed  in  the  same  way  as  the  soluble  fertilizers. 

In  an  experiment  several  organic  substances  were  mixed 
with  soil,  the  quantities  of  phosphoric  acid  and  potash  com- 
bined with  organic  matter  being  determined  before  mix- 
ing and  after  standing  for  a  year  or  more.  The  results  of 
some  of  these  experiments  are  given  in  the  following  table : 

Table  23.  —  Combinations  op  Phosphoric  Acid  and  Potash 
with  Organic  Matter  Produced  by  Mixing  Organic 
Matter  with  Soil 


Experiment  with  cow  manure  and  soil 

In  original  manure  and  soil     . 

In  mixture  after  standing  .... 

Gain  in  organic  form 

Experiment  with  green  clover 

In  original  soil  and  clover  .... 

In  mixture  after  standing  .... 

Gain  in  organic  form 

Experiment  with  meat  scrap 

In  original  soil  and  meat  scrap    .     . 

In  mixture  after  standing  .... 

Gain  in  organic  form 


Phosphoric 
Acid  Grams 


1.17 
1.62 

0.45 

3.21 
3.74 
0.53  loss 


1.07 
1.18 
0.11 


Potash 
Grams 


1.06 
1.27 
0.21 

5.26 
4.93 
0.33 

0.25 
0.36 
0.11 


When  the  organic  compounds  thus  formed  undergo  further 
decay  the  inorganic  plant-food  materials  become  available. 

119.  Loss  of  plant-food  material  in  drainage  water.  — 
The  drainage  water  from  cultivated  fields  in  humid  regions, 
and  to  a  less  extent  in  semi-arid  and  arid  regions,  except 
where  irrigation  is  practiced,  carries  off  very  considerable 
quantities  of  plant-food  material.  When  it  is  considered 
that  soil  is  constantly  subjected  to  leaching  by  rainwater 
passing  through  it,  that  this  amounts  to  many  tons  of  water 
in  the  course  of  a  year  on  every  acre  of  land,  and  that  a  water 
extract  of  soil  always  contains  some  of  each  of  the  substances 


PLANT-FOOD   MATERIALS   IN  SOILS 


103 


required  for  plant  growth,  it  is  not  hard  to  realize  that  there 
must  result  a  constant  and  significant  loss  of  fertility.  The 
plant-food  materials  lost  in  largest  quantity  are  lime,  mag- 
nesia, potash,  nitrogen  and  sulfur.  Phosphoric  acid  is 
not  removed  in  large  quantity  from  any  soil  and  appears 
only  in  traces  in  the  drainage  water  of  most  soils. 

120.  Quantities  of  plant-food  materials  in  drainage.  — 
The  quantities  of  plant-food  materials  that  are  removed 
from  soil  in  the  course  of  a  year  will  depend  on  a  variety  of 
conditions  and,  to  some  extent,  these  and  the  total  losses 
that  may  be  expected  are  indicated  by  the  following  table, 
which  is  based  on  the  annual  average  loss  for  a  period  of 
five  years  from  a  Dunkirk  clay  loam  soil  contained  in  tanks 
four  feet  deep  and  four  feet  two  inches  square. 

Table   24.  —  Number   of   Pounds   of  Plant-Pood   Materials 
Removed  in  Drainage  Water  from  One  Acre  of  Land 


Tank 
No. 

Crop 

Fertilizer 

Lime 

Mag- 
nesia 

Pot- 
ash 

Nitro- 
gen 

Sul- 
fur 

3 

4 

11 

Rotation 
No  vegetation 
Rotation 

No  fertilizer 

No  fertilizer 

Sulfate    of 

Potash 

281 
519 

298 

50 

99 
81 

64 

88 
53 

7 
102 

5 

32 
45 

56 

121.  Effect  of  crop  growth  on  loss  of  plant  nutrients  in 
drainage.  —  It  will  be  seen  that  the  loss  of  lime  is  very  large, 
amounting  to  several  hundred  pounds  to  the  acre.  The  soil 
with  no  vegetation  has  suffered  much  more  in  this  respect 
than  has  the  soil  that  was  planted.  The  soil  that  was 
fertilized  with  sulfate  of  potash  lost  somewhat  more  lime 
than  did  the  unfertilized  soil.  The  loss  of  magnesia  followed 
the  same  course  as  did  the  lime.  More  potash  was  lost 
from  the  unplanted  soil  than  from  the  cropped,  but  the  use 
of  a  potash  fertilizer  did  not  increase  the  removal  of  potash. 

In  the  case  of  nitrogen,  the  effect  of  not  cropping  the  soil 


104 


SOILS   AND   FERTILIZERS 


is  astonishing.  The  loss  from  the  cropped  soil  is  moderate, 
but  from  the  unplanted  soil  it  is  excessive.  The  loss  of  sulfur 
is  decreased  by  cropping,  and  much  increased  by  fertilizing 
with  sulfate  of  potash. 

The  loss  of  lime  and  nitrogen  in  the  uncropped  soil  as 
compared  with  the  one  that  was  cropped  is  greater  than 
the  quantity  that  would  have  been  removed  by  ordinary 
crops.  Consequently  there  is  an  actual  saving  of  these 
plant-food  materials  when  crops  are  produced. 

122.  Effect  of  fertilizers  on  loss  of  plant-food  materials 
in  drainage.  —  We  have  seen  that  the  effect  of  sulfate  of 
potash  was  to  increase  the  loss  of  lime,  magnesia  and  sulfur. 
In  general,  the  result  of  fertilizer  applications  is  similar  to 
that  shown  above.  This  is  borne  out  by  experiments  con- 
ducted at  the  Rothamsted  Experimental  Station  in  which 
drainage  was  collected  from  plats  treated  with  different 
fertilizers.  The  total  flow  of  drainage  water  from  these 
plats  was  not  measured,  but  the  composition  of  the  water 
indicates  the  effect  of  the  fertilizers. 

Table  25.  —  Composition  of  Drainage  Water  from    Wheat 
Plats,  Rothamsted  Experiment  Station 


Plat 

Manures  Applied,  Rate 

Parts  per  Million 

No. 

Lime 

Magnesia 

Potash 

Nitrogen 

2 

Farm  manure,  14  tons     . 

147.4 

4.9 

5.4 

16.3 

3  and  4 

No  manure 

98.1 

5.1 

1.7 

4.0 

5 

Minerals  only    .... 

124.3 

6.4 

5.4 

5.2 

6 

Minerals  +  200  lbs.  am- 

monium salts      .     .     . 

143.9 

7.9 

4.4 

8.7 

8 

Minerals  +  600  lbs.  am- 

monium salts      .     .     . 

197.3 

8.9 

2.7 

17.2 

9 

Minerals  +  550    lbs.    ni- 

trate of  soda  .... 

118.1 

5.9 

4.1 

18.6 

13 

Ammonium  salts  +  super- 
phosphate +  sulfate  of 

potash 

201.4 

9.3 

3.3 

17.6 

PLANT-FOOD   MATERIALS  IN  SOILS  105 

Without  going  over  this  table  in  detail,  it  may  be  noticed 
that  the  effect  of  both  farm  manure  and  commercial  fertiliz- 
ers is  to  increase  the  percentage  of  plant-food  materials  in 
the  drainage  water. 

123.  Drainage  water  from  different  soils.  —  The  composi- 
tion of  the  drainage  water  varies  with  different  soils. 
Table  20  in  which  the  composition  of  the  drainage  water 
from  Dunkirk  clay  loam  and  Volusia  silt  loam  is  given,  is 
an  illustration  of  the  very  considerable  differences  that 
may  occur  in  this  respect.  The  more  productive  soil  has 
lost  the  greater  quantity  of  plant-food  material.  The  rates 
of  loss,  however,  are  not  proportional  to  the  amounts  of 
plant  nutrients  that  the  soils  contain.  The  Dunkirk  soil 
contains  less  nitrogen  than  the  Volusia,  but  has  lost  more  in 
the  drainage  water. 

124.  Absorption  of  food  materials  by  plants.  —  It  is  only 
when  substances  are  in  solution  that  they  may  be  absorbed 
by  agricultural  plants.  This  means  that  the  soil  from  which 
plants  draw  their  nourishment  must  contain  water.  Plants 
absorb  both  water  and  nutrient  salts  through  their  roots, 
more  especially  through  the  root-hairs,  as  these  have  very 
delicate  walls  through  which  solutions  may  readily  pass. 
The  movements  of  water  and  of  salts  through  the  walls  of  the 
root-hairs  are  independent  of  each  other.  When  the  weather 
is  very  hot  and  dry,  a  larger  proportion  of  water  to  salts  will 
pass  into  the  roots  than  when  the  weather  is  cool  and  moist. 

125.  How  plants  absorb  nutrients.  —  When  a  solution 
of  plant  nutrients  is  brought  in  contact  with  roots,  there  is 
a  tendency  for  the  solution  in  the  inside  of  the  root  and  that 
on  the  outside  to  become  of  the  same  strength  for  each  par- 
ticular substance  in  the  solution.  Thus,  if  there  is  much 
available  nitrogen  in  the  solution,  it  will  be  absorbed  in 
greater  quantity  than  if  there  were  very  little.  Then,  when 
the  nitrogen  in  the  plant  juice  is  utilized  by  the  plant  to 


106 


SOILS   AND   FERTILIZERS 


form  tissue,  it  is  removed  from  the  juice  and  more  nitrogen 
is  absorbed  to  reestablish  equilibrium. 

The  substances  that  are  used  by  plants  in  large  amounts 
are  absorbed  in  greater  quantity  than  those  that  are  not 
required  in  making  tissue,  or  in  other  ways  removed  from 
solution  in  the  plant  juices.  The  unused  substances  that 
remain  in  the  plant  juices  prevent,  by  their  presence,  the 
further  absorption  of  those  particular  substances  from  the 
soil  water.  It  is  important  that  substances  like  nitrogen, 
phosphoric  acid,  potash  and  lime  shall  be  present  in  abundant 
quantities  in  the  solution  from  which  crops  draw  their 
nourishment. 

126.  How  roots  aid  in  solution  of  soil.  —  In  addition  to 
their  function  in  the  absorption  of  plant  nutrients,  there 
can  be  no  doubt  that  roots  aid  in  the  solution  of  these  nutri- 
ents from  the  soil.  One  way  is  by  the  excretion  of  carbon 
dioxide,  which  when  dissolved  in  water  is  an  excellent  solvent 
for  such  substances  as  lime,  potash  and  even  phosphoric 
acid  when  present  in  certain  forms.  The  following  table 
shows  the  percentage  of  carbon  dioxide  in  air  drawn  from 
the  bottom  of  the  large  soil  tanks  that  have  previously  been 
mentioned. '  One  of  these  tanks  produced  a  crop  of  corn 
during  the  summer  when  the  analyses  were  made,  the  other 
tank  was  kept  bare  of  vegetation. 


Table  26. 


-  Percentage  of  Carbon  Dioxide  in   Air  of  Soil 
Planted  to  Corn  and  of  Bare  Soil 


Date  of  Analysis 

Planted  Soil 

Unplanted  Soil 

Difference 

Aug.  19     ...     . 
Aug.  23     ...     . 
Aug.  26     .     .     .     . 
Aug.  30     ...     . 
Sept.  2      .     .     .     . 

3.42 
3.53 
3.44 
3.03 
3.28 

2.45 
2.00 
2.37 
2.04 
2.17 

.97 
1.53 
1.07 

.99 
1.11 

PLANT-FOOD  MATERIALS  IN  SOILS  107 

It  is  apparent  that  the  effect  of  the  growth  of  plants  has 
been  to  increase  the  amount  of  carbon  dioxide  in  the  soil 
air.  The  figures  represent  the  period  of  the  greatest  pro- 
duction of  carbon  dioxide  by  the  corn  plant. 

127.  Production  of  carbon  dioxide  by  microorganisms. 
— ■  In  addition  to  the  carbon  dioxide  excreted  from  roots, 
there  are  large  quantities  produced  by  microorganisms  that 
exist  in  soils.  These  organisms  are  concerned  in  the  decom- 
position of  organic  matter,  and  one  final  product  of  such 
action  is  carbon  dioxide.  It  has  been  estimated  that  in 
one  acre  of  soil  to  a  depth  of  sixteen  inches,  there  are  sixty- 
eight  pounds  of  carbon  dioxide  produced  by  bacteria  and 
fifty-four  pounds  excreted  by  roots  during  the  growing 
season. 

128.  Solvent  action  of  roots  in  other  ways.  —  Many  in- 
vestigators think  that  the  large  quantities  of  mineral  matter 
that  plants  remove  from  soils  could  not  be  obtained  from 
the  water  solution  even  with  the  aid  of  carbon  dioxide. 
Several  different  ways  have  been  suggested  by  which  plants 
may  assist  in  rendering  soluble  the  nutrients  contained 
in  soils.  It  will  not  be  necessary  to  discuss  these  as  there 
has  been  no  definite  and  conclusive  outcome  to  the  investi- 
gation of  the  subject.  The  indications  are,  however,  very 
strong  that  the  plant  aids  in  obtaining  its  food  material  in 
some  way  or  ways  other  than  by  the  excretion  of  carbon 
dioxide. 

129.  Difference  in  absorptive  power  of  crops.  —  Crops 
differ  greatly  in  their  ability  to  draw  nourishment  from  the 
soil.  The  difference  between  the  quantities  of  nitrogen, 
phosphoric  acid  and  potash  taken  up  by  a  corn  crop  of 
average  size  and  a  wheat  crop  of  average  size  is  very 
striking.  In  Table  27  it  may  be  seen  that  two  tons  of 
red  clover  contain  three  times  as  much  potash,  nearly  ten 
times  as  much  lime,  and  somewhat  more  phosphoric  acid 


108  SOILS   AND   FERTILIZERS 

than  does  a  crop  of  thirty  bushels  of  wheat,  including  the 
straw. 

The  ability  of  any  kind  of  plant  to  secure  nutriment  from 
the  soil  depends  on  a  number  of  factors  which  need  not  be 
discussed  here.  According  to  their  ability  in  this  direction, 
plants  have  been  popularly  classified  as  "  weak  feeders  " 
and  "  strong  feeders."  To  the  former  belong  such  crops 
as  wheat  and  onions,  which  require  very  careful  soil  prep- 
aration and  manuring.  In  the  latter  class  are  maize, 
oats  and  cabbage  which  demand  relatively  less  care.  In 
the  manuring  and  rotating  of  crops,  this  difference  in  ability 
to  obtain  nutriment  must  be  considered,  in  order  not  only 
to  secure  the  maximum  effect  on  the  crop  manured,  but 
also  to  get  the  greatest  residual  effect  of  the  manure  on  suc- 
ceeding crops. 

130.  Substances  needed  by  plants  and  substances  merely 
absorbed.  —  Some  substances  found  in  soils  and  absorbed 
by  plants  are  used  for  the  formation  of  plant  tissue,  and 
hence  are  indispensable.  Other  soil  constituents,  although 
absorbed  by  plants  to  sufficient  extent  to  be  found  in  their 
ash,  are  not  essential  to  a  normal  growth  of  crops.  The 
substances  that  are  essential  are  generally  present  in  plants 
in  considerable  quantities,  because  they  constitute  a  part 
of  the  plant  tissue. 

131.  Quantities  of  plant-food  materials  removed  by  crops. 
—  When  crops  are  removed  from  the  land,  they  carry  in 
their  tissues  considerable  quantities  of  plant-food  materials. 
The  drain  on  the  total  supply  may  be  serious  if  the  soil  is 
not  well  supplied  with  these  substances.  The  larger  the 
yield  of  crops  the  greater  the  quantities  of  plant  nutrients 
they  are  likely  to  contain.  The  following  table  shows  the 
quantities  of  nitrogen,  potash,  phosphoric  acid  and  lime 
removed  from  an  acre  of  land  by  some  of  the  common  crops. 
The  entire  harvested  crop  is  included : 


PLANT-FOOD   MATERIALS  IN  SOILS 


109 


Table  27.  —  Number  of  Pounds  of  Nitrogen,  Potash,  Lime 
and  Phosphoric  Acid  Removed  from  One  Acre  of  Soil  by 
Certain  Crops 


Crop 

Yield 

Nitrogen 

Potash 

Lime 

Phosphoric 
Acid 

Wheat     .     .     . 

30  bushels 

48 

28.8 

9.2 

21.1 

Barley     .     .     . 

40  bushels 

48 

35.7 

9.2 

20.7 

Oats  .     .     .     . 

45  bushels 

55 

46.1 

11.6 

19.4 

Corn  .... 

30  bushels 

43 

36.3 

— 

18.0 

Meadow  hay    . 

1|  tons 

49 

50.9 

32.1 

12.3 

Red  clover 

2  tons 

102 

83.4 

90.1 

24.9 

Potatoes      .     . 

6  tons 

47 

76.5 

3.4 

21.5 

Turnips  .     .     . 

17  tons 

192 

148.8 

74.0 

33.1 

While  these  are  only  a  few  of  the  cultivated  crops,  they 
give  some  idea  of  the  quantities  of  plant-food  materials 
removed  from  soils  by  ordinary  cropping.  The  nitrogen 
removed  by  red  clover  is  partly  taken  from  the  air  and  conse- 
quently the  draft  on  the  soil  supply  is  not  so  great  as  would 
be  indicated  by  the  figure  here  given. 

132.  Possible  exhaustion  of  mineral  nutrients.  —  Com- 
paring the  figures  given  above  with  those  in  Table  17 
it  is  evident  that  there  is  a  supply  in  most  arable  soils 
that  will  afford  nutriment  for  average  crops  for  a  very  long 
period  of  time.  On  the  other  hand,  when  it  is  considered 
that  the  soil  must  be  depended  on  to  furnish  food  for  hu- 
manity and  domestic  animals  as  long  as  they  shall  continue 
to  inhabit  the  earth,  at  least  so  far  as  is  now  known,  the 
very  apparent  possibility  of  exhausting,  even  in  a  period 
of  several  hundred  years,  the  supply  of  plant  nutrients 
becomes  a  matter  of  grave  concern. 

The  visible  sources  of  supply  to  replace  or  to  supplement 
the  nutrients  in  the  soil  now  cultivated  are,  for  the  mineral 
substances,  the  subsoil  and  the  natural  deposits  of  phosphates, 
potash  salts  and  limestone ;  and  for  nitrogen,  deposits  of 
nitrates,  the  by-product  of  coal  distillation  and  the  nitrogen 


110  SOILS  AND   FERTILIZERS 

of  the  atmosphere.  The  last  of  these  is  inexhaustible, 
and  the  exhaustion  of  the  soil  nitrogen  supply,  which  a  few 
years  ago  was  thought  by  some  to  be  a  matter  of  less  than 
half  a  century,  has  now  ceased  to  cause  any  apprehension. 
The  conservation  or  extension  of  the  supply  of  mineral 
nutrients  is  now  of  supreme  importance.  The  utilization 
of  city  refuse  and  the  discovery  of  new  mineral  deposits 
are  developments  well  within  the  range  of  possibility,  but 
neither  of  these  promises  to  afford  more  than  partial  relief. 
The  utilization  of  the  subsoil  through  the  gradual  removal 
by  natural  agencies  of  the  topsoil  will,  without  doubt,  tend 
to  constantly  renew  the  supply.  The  removal  of  topsoil 
by  wind  and  erosion  is,  even  on  level  land,  a  very  considerable 
factor.  The  large  amount  of  sediment  carried  in  streams  im- 
mediately after  a  rain,  especially  in  summer,  gives  some  idea  of 
the  extent  of  this  shifting.  This  affects  chiefly  the  surface  soil, 
and  thereby  brings  the  subsoil  into  the  range  of  root  action. 
There  is  little  doubt  that  a  moderate  supply  of  plant- 
food  materials  will  always  be  available  in  most  soils,  but  for 
progressive  agriculture  manures  must  be  used. 

QUESTIONS 

1.  How  does  the  total  quantity  of  plant-food  materials  in  soils 
compare  with  the  total  weight  of  soil  ? 

2.  Are  the  percentages  of  nitrogen,  phosphoric  acid  and  potash 
uniform  in  different  soils,  or  do  they  differ  ? 

3.  Is  there  a  direct  relation  between  the  productiveness  of  a  soil 
and  its  content  of  plant-food  materials  ? 

4.  What  is  meant  by  available  and  unavailable  plant  nutrients  ? 

5.  Name  some  of  the  factors  that  influence  the  availability  of 
plant  nutrients  in  soils. 

6.  Why  is  it  not  always  possible  to  determine  by  chemical  analy- 
sis the  degree  of  productiveness  of  a  soil  ? 

7.  Explain  what  is  meant  by  the  absorptive  properties  of  soil  for 
soluble  fertilizers. 

8.  Explain  what  is  meant  by  selective  absorption. 


PLANT-FOOD   MATERIALS  IN  SOILS  111 

9.    Explain  the  availability  of  absorbed  fertilizers. 

10.  What  two  constituents  are  removed  in  greatest  quantity 
by  drainage  water  from  an  unplanted  soil  ? 

11.  Explain  how  roots  aid  in  the  solution  of  soil. 

LABORATORY   EXERCISES 

Exercise  I.  —  Soluble  matter  of  soil. 

Materials.  —  A  very  rich  soil,  filter  paper  and  funnel,  evaporat- 
ing dish,  flame,  dilute  hydrochloric  acid. 

Procedure.  —  Place  a  small  amount  of  a  rich  soil  on  a  filter  paper 
held  in  a  funnel  and  leach  with  distilled  water,  catching  percolate 
in  an  evaporating  dish.  Evaporate  percolate  to  dryness  and  exam- 
ine residue.  Is  it  large  or  small  in  amount  ?  Treat  with  a  few 
drops  of  dilute  acid.  Finally  heat  over  a  flame.  Explain  results. 
This  soluble  matter  is  the  most  valuable  portion  of  the  soil. 

Exercise  II.  —  Absorptive  power  of  soil  for  dyes. 

Materials.  —  Soil,  filter  paper,  funnel,  solution  of  gentian  violet. 

Procedure.  —  Place  a  small  amount  of  soil  on  a  filter  paper  in  a  fun- 
nel and  treat  with  a  solution  of  gentian  violet.  Note  that  the  water 
comes  through  clear  for  a  considerable  period  indicating  the  high  ab- 
sorptive power  of  the  soil  for  this  dye.  The  capacity  of  the  soil  to 
absorb  soluble  matter  prevents  heavy  losses  of  plant-food  materials. 

Exercise  III.  —  Selective  absorption  by  the  soil. 

Materials.  —  Soil,  filter  paper  and  funnel,  solution  of  gentian 
violet  and  solution  of  eosin. 

Procedure.  —  Proceed  in  the  same  way  as  Exercise  II,  comparing 
the  absorptive  power  of  portions  of  the  same  soil  for  the  two  dyes. 
Note  the  difference.  The  soil  varies  in  its  absorptive  power  with 
different  materials.  For  instance,  the  soil  absorbs  acid  phosphate 
much  more  strongly  than  sodium  nitrate. 

Exercise  IV.  —  Absorptive  power  of  the  soil  for  gas. 

Materials.  —  A  moist  loam  rich  in  organic  matter,  a  flask  or 
bottle,  concentrated  ammonia. 

Procedure.  —  Place  in  a  flask  or  bottle  a  quantity  of  moist  soil. 
Pour  in  a  few  drops  of  ammonia.  Note  strong  odor.  Stopper 
bottle  and  shake.  Allow  to  stand  for  half  an  hour  with  several  shak- 
ings.    Open  and  note  odor. 

The  absorptive  power  of  the  soil  for  ammonia,  oxygen  and  other 
gases  is  a  very  important  function.     Explain  why  this  is  true. 


CHAPTER  VIII 
ACID  SOILS  AND  ALKALI  SOILS 

Some  soils  are  termed  acid,  or  sour  soils.  They  are  so 
called  because  they  give  the  same  tests  with  certain  chemi- 
cals that  are  obtained  with  vinegar  and  other  acids.  A 
common  test  for  acids  is  to  bring  them  in  contact  with  blue 
litmus  paper,  and  if  the  material  is  acid  the  paper  is  colored 
red.  Soils  that  are  strongly  acid  will  also  do  this.  Another 
property  of  acid  materials  is  that,  if  sufficient  quick-lime 
is  brought  in  contact  with  them  they  will  no  longer  color 
blue  litmus  paper  red.  This  may  be  tried  by  slowly  stirring 
quick-lime  into  vinegar  and  testing  it  occasionally  with 
litmus  paper.  If  sufficient  quick-lime  be  added  to  an  acid 
soil,  it  will  no  longer  turn  blue  litmus  paper  red. 

Whether  a  soil  is  acid  or  not  is  a  matter  of  practical  im- 
portance, because  some  plants  do  not  grow  so  well  on  sour 
soils  as  they  do  on  soils  that  are  neutral  or  alkaline ;  on  the 
other  hand  some  crops  prefer  an  acid  soil. 

133.  Nature  of  soil  acidity.  —  There  are  two  kinds  of 
soil  acidity  (1)  when  acids  are  present  that  have  been  formed 
by  fermentation  of  organic  matter  in  the  soil,  (2)  when  there 
is  a  deficiency  of  such  material  as  lime  or  potash.  In  either 
case  the  soil  will  color  blue  litmus  paper  red. 

134.  Positive  acidity.  —  The  condition  of  soil  first  men- 
tioned above  has  been  termed  positive  acidity.  It  arises 
from  the  decomposition  of  organic  matter  when  soil  condi- 
tions are  not  favorable  to  the  proper  breaking  down  of  the 
intermediate  substances.     An  insufficient  air  supply  caused 

112 


ACID   SOILS   AND   ALKALI   SOILS  113 

by  saturation  or  compaction  of  the  soil,  or  a  lack  of  lime,  may 
lead  to  the  formation  of  these  acids.  Acid  soils  to  which 
certain  organic  acids  have  been  added  were  found  to  be 
unfavorable  to  the  growth  of  plants  like  wheat,  while  the 
same  soil,  to  which  lime  had  been  applied,  produced  a  much 
better  growth.  Lime  overcomes  the  injurious  effect  of  this 
kind  of  acidity. 

135.  Negative  acidity.  —  When  a  soil  contains  no  free 
acids  but  is  sour  in  its  relations  to  plant  growth,  it  may  be 
said  to  possess  negative  acidity.  Negative  acidity  is  coun- 
teracted by  the  application  of  lime  just  as  is  positive  acidity. 
The  condition  that  renders  the  soil  acid  is  a  lack  of  sub- 
stances like  lime,  magnesia,  soda  and  potash.  Any  one  of 
these  four  substances  is  called  a  base.  Lime,  being  the  cheap- 
est of  these  to  apply,  is  the  usual  corrective.  The  injurious 
action  of  soil  acidity  on  plant  growth  has  been  attributed 
to  one  or  more  of  the  following  causes :  (1)  lack  of  lime  to 
overcome  organic  acids  when  they  are  formed ;  (2)  absence 
of  sufficient  carbonate  of  lime ;  (3)  great  absorbent  properties 
that  cause  the  soil  to  compete  with  plants  in  their  attempt 
to  draw  plant-food  materials  from  the  soil. 

136.  Ways  by  which  soils  become  sour.  —  In  regions  of 
ample  rainfall  there  is  always  a  tendency  for  soils  to  become 
sour,  and  unless  they  originally  contain  large  quantities 
of  lime,  or  are  of  recent  formation,  they  are  likely  to  be  in 
need  of  lime.  This  tendency  may  be  due  to  any  one  or  more 
of  the  following  causes:  (1)  removal  of  lime  and  similar 
substances  in  drainage  water;  (2)  removal  of  these  sub- 
stances by  plants;  (3)  accumulation  of  acids  contained  in 
fertilizers  applied  to  the  soil ;  (4)  formation  of  organic  acids 
from  plant  remains. 

137.  Drainage  as  a  cause  of  acidity.  —  The  chief  cause  of 
soil  acidity  is  doubtless  the  removal  of  lime,  magnesia,  soda 
and  potash  from  soil  by  the  water  that  percolates  through 


114  SOILS   AND   FERTILIZERS 

the  soil  and  passes  off  as  drainage.  The  quantities  of  these 
materials  that  are  annually  lost  from  an  acre  of  soil,  as  found 
by  lysimeter  experiments,  are  shown  in  Table  24. 

It  will  be  noticed  that  there  is  a  much  greater  loss  from  the 
unplanted  soil  than  from  the  planted.  The  quantities  of 
these  materials  taken  up  by  some  crops  is  much  less  than  the 
difference  between  the  quantities  in  the  drainage  in  the 
planted  and  unplanted  soil,  hence  the  growth  of  these  crops 
on  land  is  really  a  means  of  saving  lime. 

138.  Effect  of  plant  growth  on  soil  acidity.  —  Plant  growth 
may  promote  soil  acidity  in  the  following  ways :  (1)  by  re- 
moval of  the  bases  in  the  ash  of  the  plants ;  (2)  by  leaving 
in  the  soil  the  acids  with  which  these  bases  were  combined  ; 
(3)  by  formation  of  organic  acids  during  decomposition  of 
plant  remains. 

It  will  be  seen  from  Table  27  that  the  quantities  of 
potash  and  lime  removed  in  crops  of  average  size  vary 
considerably  and  in  some  cases  are  very  large.  When, 
as  in  a  state  of  nature,  the  vegetation  on  the  land  is  returned 
to  it  after  life  ceases,  and  its  organic  material  is  again 
incorporated  with  the  soil,  there  is  no  loss  in  this  way,  but 
in  ordinary  farming  most  of  the  above  ground  portion  of 
the  crop  is  removed  from  the  land.  The  manure  of  growing 
animals  returns  to  the  soil  only  a  small  proportion  of  the 
lime  that  was  originally  in  the  plants  because  the  animal 
has  used  it,  and  the  potash  is  likely  to  be  leached  from  the 
manure  unless  it  is  carefully  handled. 

Crops  in  growing  remove  more  potash  and  other  bases 
from  the  soil  than  they  do  the  acid-producing  substances, 
which  latter  are  left  in  the  soil  and  contribute  still  more  to 
its  tendency  to  assume  an  acid  condition. 

139.  Effect  of  fertilizers  on  soil  acidity.  —  It  has  been 
shown  very  conclusively  that  the  continued  use  of  considerable 
quantities  of  sulfate  of  ammonia  on  land  may  result  in  bring- 


ACID   SOILS   AND   ALKALI   SOILS  115 

ing  about  an  acid  condition.  In  the  case  of  this  fertilizer 
the  ammonia  is  absorbed  either  directly  or  indirectly  and 
most  of  the  sulfate,  which  is  an  acid,  remains  in  the  soil. 
Probably  no  other  fertilizer  is  so  active  in  producing  acidity, 
but  it  is  possible  that  sulfate  of  potash  or  muriate  of  potash 
or  gypsum  may, -in  less  degree,  have  the  same  tendencj'. 

The  use  of  free  sulfur  for  combating  fungous  diseases  may 
also  lead  to  the  formation  of  a  sour  soil. 

140.  Effect  of  green-manures  on  acidity.  —  In  soils  defi- 
cient in  lime  the  incorporation  of  green-manure  crops  has 
been  thought  to  produce  temporarily  an  acid  condition. 
It  is  during  the  early  stages  of  fermentation  in  the  soil  that 
the  acids  are  formed.  When  further  decomposition  pro- 
ceeds, the  acids  are  broken  up  and  acidity  disappears.  This 
condition  has  been  noticed  mainly  in  the  South  Atlantic 
states.  Where  it  has  been  found  to  occur,  there  is  some  ad- 
vantage to  be  gained  from  plowing  under  the  green-manure 
as  long  as  possible  before  planting  the  next  crop. 

141.  Weeds  that  flourish  on  sour  soils.  —  Whether  a  soil 
is  acid  or  not  will  make  a  great  difference  in  the  kinds  of 
plants  that  will  thrive  on  it.  Certain  weeds  will  generally 
be  found  growing  on  sour  soil  and  the  presence  of  these  in 
large  numbers  may  be  taken  as  evidence  that  the  soil  needs 
lime.  Weeds  that  appear  to  flourish  on  acid  soils  may  do 
so  either  because  they  are  physiologically  adapted  to  an 
acid  condition,  or  because  other  vegetation  does  not  thrive, 
and  hence  these  particular  weeds  have  less  competition  on 
this  soil.  The  weeds  that  in  one  part  of  the  country  or 
another  may  be  considered  to  indicate  an  acid  soil  are  as 
follows : 

Sheep  sorrel  Corn  spurry 

Paintbrush  Wood  horsetail 

Daisy  Plantain 

Horsetail  rush  Goose-grass 


116 


SOILS   AND   FERTILIZERS 


142.  Crops  adapted  to  sour  soils.  —  There  are  a  consider- 
able number  of  plants,  other  than  weeds,  that  grow  well  on 
sour  soils,  some,  in  fact,  thriving  better  when  the  soil  is 
acid  than  when  it  is  not  so.  The  following  is  a  list  of  those 
that  have  been  found  to  be  adapted  to  soils  of  this  kind : 


Blueberry 

Rhode  Island  bent-grass 

Rye 

Cranberry 

Cowpea 

Millet 

Strawberry 

Soy  bean 

Buckwheat 

Blackberry 

Castor  bean 

Carrot 

Raspberry 

Hairy  vetch 

Lupine 

Watermelon 

Crimson  clover 

Serradella 

Turnip 

Potato 

Radish 

Redtop 

Sweet  potato 

Velvet  bean 

This  list  affords  a  sufficient  number  of  plants  to  permit  of 
a  largely  diversified  cropping  system  on  sour  soil,  should  it 
be  undesirable,  or  very  expensive,  to  put  lime  on  the  land. 
The  considerable  number  of  legumes  in  the  list  would  admit 
of  soil  improvement  through  their  use. 

143.  Crops  that  are  injured  by  acid  soils.  —  While  there 
is  a  considerable  number  of  agricultural  plants  that  are 
adapted  to  sour  soil,  it  is  true  that  the  greater  number  of 
the  most  important  crops  is  injured  by  such  soil.  General 
farming  can  best  be  conducted  on  soil  that  is  not  greatly 
in  need  of  lime.  One  reason  for  this  is  that  the  great  soil- 
improving  crops  —  red  clover  and  alfalfa  —  are  very  un- 
certain crops  on  acid  soils.  The  following  plants  are  injured 
by  sour  soil : 


Alfalfa 

Pumpkin 

Cucuml 

Red  clover 

Salsify 

Lettuce 

Saltbush 

Spinach 

Onion 

Timothy 

Red  beet 

Peanut 

Blue-grass 

Sorghum 

Okra 

ACID  SOILS   AND   ALKALI   SOILS  117 


Maize 

Barley 

Tobacco 

Oats 

Sugar  beet 

Kohlrabi 

Pepper 

Currant 

Eggplant 

Parsnip 

Celery 

Mangel-wurzel 

Cauliflower        Cabbage. 

Some  of  these  plants  will  grow  well  on  soil  that  is  too  sour 
for  other  crops.  For  example,  red  clover  will  grow  fairly 
well  on  soil  that  is  too  acid  to  raise  alfalfa. 

144.  Litmus  paper  test  for  soil  acidity.  —  This  test  is 
made  with  blue  litmus  paper,  which  is  brought  in  imme- 
diate contact  with  wet  soil.  A  rapid  and  decided  change 
to  red  is  taken  to  indicate  an  acid  condition  of  the  soil. 
Carbonic  acid,  which  is  always  present  in  soils,  but 
which  is  not  injurious  to  plant  growth,  is  supposed  to  give 
only  a  faint  pink  color  to  the  litmus  paper.  Various  ways 
of  bringing  the  paper  into  contact  with  the  soil  have 
been  proposed,  among  others  the  placing  of  filter  paper  or 
blotting  paper  between  the  soil  and  the  litmus  paper. 
It  has  also  been  pointed  out  that  the  acid  perspiration  of 
the  fingers  may  lead  to  a  mistaken  conclusion  that  the  soil 
is  acid. 

Much  litmus  paper  is  sold  that  is  of  very  poor  quality, 
and  an  effort  should  be  made  to  obtain  a  good  article.  When 
good  paper  is  used  and  the  test  is  carefully  made,  the  general 
experience  has  been  that  it  is  a  fairly  good,  although  not  an 
infallible,  guide  to  the  need  of  a  soil  for  lime. 

145.  Litmus  paper  and  potassium  nitrate.  —  This  is  per- 
formed in  the  same  manner  as  the  former  litmus  paper  test, 
except  for  the  substitution  of  a  saturated  solution  of  potas- 
sium nitrate  instead  of  water  for  moistening  the  soil.  It  is 
a  more  delicate  test  than  the  one  with  litmus  paper  alone. 
The  operation  consists  in  working  a  small  soil  sample  to  a 
thick  paste  with  a  saturated  solution  of  potassium  nitrate 


118  SOILS  AND   FERTILIZERS 

and  applying  the  paper  directly  to  the  soil.  If  the  soil  is 
acid,  the  potassium  will  be  absorbed  and  an  acid  or  acid  salt 
set  free,  which  will  act  on  the  litmus  paper,  giving  it  a  decided 
pink  color. 

146.  The  Truog  test.  —  In  this  test  solutions  of  calcium 
chloride  and  zinc  sulfide  are  brought  in  contact  with  the 
soil  to  be  tested  and  the  mixture  is  boiled.  If  the  soil  is 
acid,  a  gas  called  hydrogen  sulfide  is  formed  and  driven  off 
with  the  steam.  The  presence  of  this  gas  may  be  detected 
by  placing  a  strip  of  moist  lead  acetate  paper  over  the  mouth 
of  the  flask  in  which  the  soil  and  solutions  are  boiled.  The 
lead  acetate  paper  is  rapidly  darkened  by  the  hydrogen 
sulfide  gas  as  it  passes  out  of  the  flask.  Detailed  descrip- 
tions of  the  methods  for  making  these  tests  for  soil  acidity 
will  be  found  in  the  laboratory  exercises. 

147.  Alkali  soils.  —  We  have  seen  that  every  soil  is 
constantly  undergoing  decomposition,  by  which  process  a 
very  minute  fraction  becomes  soluble  every  year.  Ordi- 
narily, in  humid  regions,  this  soluble  matter  is  leached  out 
by  the  rain  water  that  percolates  through  the  soil.  In 
those  parts  of  the  world  where  the  rainfall  is  very  slight, 
and  yet  where  decomposition  of  soil  proceeds,  there  is  a 
tendency  for  the  soluble  matter  to  accumulate  in  the  soil 
where  there  is  no  drainage,  or  for  it  to  move  to  places  where 
seepage  accumulates.  A  strong  accumulation  of  such  soluble 
matter  is  known  as  alkali  because  it  usually  has  an  alkaline 
reaction,  i.e.  it  turns  red  litmus  paper  blue. 

148.  Nature  and  movements  of  alkali.  —  Because  of  its 
easy  solubility,  alkali  may  move  from  place  to  place  or  up- 
ward and  downward  in  soils.  During  periods  of  drought 
it  is  carried  upward  by  the  capillary  rise  of  the  soil  water, 
while  during  periods  of  rainfall  it  may  move  downward, 
where  it  is  out  of  range  of  roots.  The  composition  of  alkali 
varies  greatly  in  different  regions.     The  main  distinctions 


ACID  SOILS   AND   ALKALI   SOILS  119 

are  between  white  and  black  alkali.  The  former  gets  its 
name  from  the  fact  that  when  it  accumulates  on  the  surface 
of  the  ground,  as  is  very  common  in  a  dry  time,  it  has  a  white 
appearance.  The  latter,  on  the  other  hand,  is  black,  because, 
owing  to  its  caustic  nature,  it  dissolves  organic  matter  from 
the  soil,  which  gives  it  a  black  color. 

149.  Effect  of  alkali  on  crops.  —  Both  white  and  black 
alkalis  are  injurious  to  plant  growth  when  present  in  large 
quantity,  but  black  alkali  is  much  more  active  in  this  re- 
spect, as  it  attacks  plant  tissue  just  as  it  does  the  organic 
matter  in  soils.  White  alkali  injures  plants  by  withdraw- 
ing water  from  the  plant  cells  and  causing  the  plant  to 
wilt.  The  nature  of  the  salts  contained  in  the  alkali,  and 
the  species  and  even  the  individuality  of  the  plant,  de- 
termine the  amount  of  alkali  that  is  required  to  destroy  a 
crop. 

150.  Tolerance  of  different  plants  to  alkali.  —  Some  plants 
are  better  able  to  endure  the  presence  of  alkali  in  soil  than 
are  others.  This  is  due,  in  part,  to  the  natural  resistance 
of  the  plant  to  the  injurious  effect,  and  in  part  to  the  rooting 
habit  of  the  plant.  Deep-rooted  plants  are,  in  general, 
better  able  to  resist  alkali  than  are  shallow-rooted  ones, 
probably  because  some  part  of  the  root  is  in  a  less  strongly 
impregnated  part  of  the  soil. 

Of  the  cereals,  barley  and  oats  are  the  most  tolerant.  Of 
the  forage  crops,  a  number  of  valuable  grasses  are  able 
to  grow  on  soil  containing  a  considerable  quantity  of 
white  alkali.  Timothy,  smooth  brome-grass  and  alfalfa 
are  among  the  cultivated  forage  crops  most  tolerant  of 
alkali,  although  they  do  not  equal  the  native  grasses  in  this 
respect. 

The  resistance  of  a  number  of  plants  to  white  alkali,  ex- 
pressed in  pounds  to  the  acre  to  a  depth  of  four  feet,  is  as 
follows : 


120  SOILS   AND   FERTILIZERS 

Table  28.  —  Resistance  of  Crops  to  Alkali    - 


Cbop 

Total  Alkali 

Crop 

Total  Alkali 

Peaches    .     .     . 

11,280 

Barley    .     .     . 

25,520 

Rye     ...     . 

12,480 

Grapes    .     .     . 

45,760 

Apples      .     .     . 

16,120 

Sugar  beets 

59,840 

Pears   .... 

20,920 

Sorghum      .     . 

81,360 

Oranges    .     .     . 

21,840 

Alfalfa    .     .     . 

110,320 

Saltbush      .     . 

156,720 

151.  Irrigation  and  alkali.  —  Frequently  the  injurious 
presence  of  alkali  in  an  irrigated  region  has  been  discovered 
only  after  irrigation  has  been  practiced  for  a  number  of  years. 
This  is  due  to  what  is  termed  "  rise  of  alkali,"  and  comes 
about  through  the  accumulation,  near  the  surface  of  the 
soil,  of  salts  that  were  formerly  distributed  throughout 
a  depth  of  perhaps  many  feet.  Before  the  land  was  irrigated, 
the  alkali  was  distributed  through  a  great  depth  of  soil,  but 
after  water  was  turned  on,  this  was  dissolved,  and  later 
brought  to  the  surface,  as  the  soil  was  allowed  to  dry  out. 
The  upward  movement  in  such  cases  exceeds  the  downward 
because  the  descending  water  passes  largely  through  the 
non-capillary  pore  spaces,  while  the  ascending  water  passes 
entirely  through  the  capillary  spaces.  The  alkali  accumu- 
lates principally  in  the  capillary  spaces  and  hence  is  swept 
to  the  surface  in  large  quantities  by  the  upward  movement 
of  capillary  water. 

152.  Removal  of  alkali.  —  There  are  several  ways  in 
which  alkali  may  be  removed  from  soil,  among  which  are 
the  following:  (1)  leaching  with  underdrainage ;  (2)  correc- 
tion with  gypsum ;   (3)  scraping ;   (4)  flushing. 

The  first  of  these  consists  in  laying  tile  drains,  much  as  is 
done  for  draining  land  in  humid  regions,  then  flooding  the 
land  with  large  quantities  of  water,  which  dissolves  the  alkali 


ACID  SOILS   AND   ALKALI   SOILS  121 

and  carries  it  out  through  the  drains.  This  is,  by  all  means, 
the  most  effective  way  of  removing  alkali. 

Gypsum  has  been  used  for  converting  black  alkali  into 
white  alkali,  which  it  does  by  inducing  chemical  changes  in 
the  alkali.  This  may  well  be  used  when  black  alkali  land 
is  to  be  drained. 

Scraping  consists  in  allowing  alkali  to  accumulate  at  the 
surface  of  the  soil  and  then  removing  it  with  a  scraper.  This 
is  never  a  very  effective  treatment. 

Flushing  is  accomplished  by  removing  the  surface  incrusta- 
tion with  a  rapidly  moving  stream  of  water  instead  of  a 
scraper.  like  the  former  method  it  is  not  usually  an 
adequate  treatment. 

153.  Control  of  alkali.  —  Instead  of  actually  removing 
alkali  its  injurious  action  may  often  be  kept  in  check  by  keep- 
ing it  well  distributed  through  the  soil  and  not  allowing  it 
to  accumulate  near  the  surface.  This  may  be  done  by  con- 
trolling evaporation  and  by  the  cultivation  of  alkali-tolerant 
plants.  The  methods  usually  employed  for  retarding  evap- 
oration of  moisture  are  generally  applicable  for  controlling 
alkali. 

Cropping  with  alkali-tolerant  plants  naturally  suggests 
itself  as  a  means  of  combating  alkali  where  it  does  not  exist 
to  such  an  extent  as  to  interfere  with  all  crop  production. 
As  these  plants  remove  considerable  quantities  of  alkali  in 
their  ash,  they  also  serve  as  a  means  of  alkali  removal. 

QUESTIONS 

1.  Distinguish  between  positive  and  negative  acidity  in  soils. 

2.  Describe  three  ways  in  which  soil  acidity  may  be  injurious  to 
plant  growth. 

3.  State  three  ways  by  which  the  growth  of  plants  on  soil  tends 
to  make  it  become  sour. 

4.  What  is  the  effect  on  soil  acidity  of  a  continued  use  of  am- 
monium sulfate  ? 


122  SOILS   AND   FERTILIZERS 

5.  If  green-manures  are  found  to  produce  acidity  on  a  particular 
soil,  what  precaution  should  be  taken  in  using  them  ? 

6.  Name  three  or  four  weeds  whose  presence  in  large  numbers 
indicates  that  a  soil  is  acid. 

7.  Name  six  or  eight  crops  that  are  adapted  to  growth  on  sour 
soils,  and  an  equal  number  that  are  injured  by  a  sour  soil. 

8.  Describe  the  litmus  paper  test  for  the  detection  of  a  sour  soil. 

9.  Describe  the  test  with  litmus  paper  and  potassium  nitrate 
solution. 

10.  State  what  is  meant  by  an  alkali  soil. 

11.  Explain  the  difference  between  white  and  black  alkali,  and 
the  effect  of  each  on  crops. 

12.  Name  some  of  the  crops  most  tolerant  of  alkali. 

13.  Describe  four  ways  by  which  alkali  may  be  removed  from  soil. 

LABORATORY   EXERCISES 

Exercise  I.  —  Acid  soils  in  the  field. 

Plan  a  field  trip  to  a  soil  known  to  be  distinctly  acid.  Observe 
structure  of  soil,  organic  content,  character  of  crop  and,  particularly, 
character  of  other  vegetation.  It  might  be  well  to  make  a  collec- 
tion of  the  plants  which  are  supposed  to  indicate  acidity.  Take 
samples  of  this  soil  for  future  tests  for  acidity  in  the  laboratory. 

Exercise  II.  —  Litmus  paper  with  and  without  potassium  ni- 
trate. 

Materials.  —  Litmus  paper,  acid  soil,  evaporating  dish,  a  neutral 
potassium  nitrate  solution. 

To  prepare  litmus  paper  boil  litmus  powder  (1  part)  with  alcohol 
(2  parts)  for  five  minutes.  Allow  to  settle  ana*  pour  off  the  alcohol, 
thus  carrying  away  certain  dyes  of  low  sensitiveness.  To  the 
powder  now  add  five  parts  of  water.  Boil  10  minutes  and  allow 
to  stand  overnight.  Decant  liquid  and  filter  it.  This  gets  rid  of 
most  of  the  carbonates.  Now  make  acid  with  sulfuric  acid  and  bring 
back  to  required  tint  with  barium  hydrate.  Dip  narrow  strips  of 
filter  paper  into  the  solution  and  dry  on  glass.  When  dry  cut  into 
strips  of  the  required  size. 

Procedure.  —  Mix  one  portion  of  &  distinctly  acid  soil  to  a  thick 
paste  in  an  evaporating  dish  with  distilled  or  rain  water.  Allow 
to  stand  for  a  few  minutes,  then  pat  to  a  smooth  surface  and  apply 
to  it  one  end  of  a  strip  of  litmus  paper,  leaving  the  other  end  free  for 
comparison.     Press  paper  closely  in  contact  with  soil. 


ACID   SOILS   AND   ALKALI   SOILS  123 

Treat  another  small  portion  of  this  soil  in  the  same  way,  using 
a  neutral  potassium  nitrate  solution  instead  of  distilled  water. 

Observe  the  rate  of  change  of  color  of  the  litmus  paper  with  and 
without  potassium  ni- 
trate. n  & 

Exercise    III. 
Litmus  paper  test. 

Materials.  —  Same 
as  Exercise  II. 

Procedure.  —  Test 
a  number  of  different  Fig.  21.  —  Procedure  in  the  litmus  paper  test, 
soils.  The  students  («)  small  evaporating  dish,  (6)  soil  worked  to  a 
should   be   encouraged  *^n  Paste  w*tn  Pure  water  or  a  neutral  potassium 

,    .  , .     .  nitrate  solution,  (c)  the  litmus  paper  in  position, 

to   bring  m   their  own  with  one  end  free  for  comparison, 
samples.  Note  whether 

there  appears  to  be  a  difference  in  degree  of  acidity  of  these  soils 
as  indicated  by  the  quickness  with  which  the  litmus  paper  turns  red 
and  the  shade  of  red  produced. 

Exercise  IV.  —  Test  for  soil  carbonates. 

Materials.  —  Soil,  evaporating  dish,  dilute  hydrochloric  acid. 

Procedure.  —  Treat  a  small  portion  of  the  soil  to  be  tested  with 
dilute  hydrochloric  acid.  Effervescence  indicates  the  presence  of 
carbonates.  A  soil  so  reacting  needs  no  lime.  If  no  reaction  oc- 
curs, test  with  litmus  paper,  as  the  soil  may  be  alkaline,  neutral 
or  acid. 

Exercise  V.  —  Ammonia  test  for  acidity. 

Materials.  —  Soil,  8  oz.  bottle,  concentrated  ammonia. 

Procedure.  —  Place  about  25  grams  of  soil  in  an  8  oz.  bottle  and 
add  10  c.c.  of  ammonia.  Fill  two-thirds  full  with  distilled  or  rain 
water.  Shake  well  and  allow  to  stand  overnight.  A  darkening 
of  the  supernatant  liquid  is  an  indication  of  the  lack  of  lime. 

This  method  is  not  a  quantitative  one  because  the  degree  of 
darkening  of  the  liquid  depends  on  the  amount  of  organic  matter 
present  rather  than  the  degree  of  acidity. 

Exercise  VI.  —  Zinc  sulfide  test  for  acidity.     (See  Fig.  22.) 

Materials.  —  Soil,  250  to  300  c.c.  Erlenmeyer  flask,  tripod  and 
wire  gauze,  flame,  calcium  chloride-zinc  sulfide  solution,  lead  ace- 
tate paper. 

The  calcium  chloride-zinc  sulfide  reagent  is  made  up  as  follows : 
50  grams  of  neutral  calcium  chloride  plus  5  grams  of  zinc  sulfide 


124 


SOILS   AND   FERTILIZERS 


is  added  to  250  c.c.  of  distilled  water.     The  solution  should  be 

shaken  well  each  time  before  using  as  the  zinc  sulfide  is  insoluble  and 

tends  to  sink  to  the  bottom  of  the  vessel. 

The  lead  acetate  paper  is  made  by  dipping  strips  of  filter  paper 

into  a  saturated  solution  of  lead  acetate  and  drying. 

Procedure.  —  Place  in  a  250  or  300  c.c. 
Erlenmeyer  flask  a  10  gram  sample  (well 
pulverized)  of  the  soil  to  be  tested.  Now 
add  5  c.c.  of  the  calcium  chlo  ide-zinc  sulfide 
reagent,  the  former  being  in  solution  and 
the  latter  in  suspension.  Add  75  c.c.  of  dis- 
tilled water.  Place  on  a  wire  gauze  over  a 
flame  and  bring  to  boiling;  Boil  exactly  one 
minute,  being  careful  not  to  allow  the  sample 
to  froth  over. 

The  boiling  having  become  constant  and 
the  C02  being  driven  off,  lay  over  the  mouth 
of  the  flask  a  strip  of  lead  acetate  paper 
moistened  in  distilled  water.  Allow  it  to 
remain  there  exactly  three  minutes.  The  test 
is  now  complete  and  acidity  is  indicated  by 
the  blackening  of  the  paper. 

Exercise  VII.  —  Incrustation  of  "  al- 
kali "  by  capillary  action. 

Materials.  —  Sandy  loam,  lamp  chimney, 
pan,  salt. 

Procedure.  —  Prepare  a  lamp  chimney  by 
neatly  tying  over  the  end  two  thicknesses  of 
cheesecloth.  Fill  with  sandy  loam.  Set  the 
chimney  now  prepared  into  a  solution  of  common  salt.  The  salt 
solution  will  soon  rise  through  the  column  by  capillary  action  and 
evaporation  will  take  place  f  om  the  soil.  This  will  soon  cause 
an  incrustation  of  "  white  alkali "  on  the  surface  of  the  soil 

Explain  this  experiment  in  relation  to  irrigation  practice  and 
moisture  conservation  under  arid  conditions. 


Fig.  22.  —  Apparatus 
for  the  zinc  sulfide  test 
for  soil  acidity,  (a)  lead 
acetate  paper  in  posi- 
tion, (6)  flask,  (c)  soil 
treated  with  calcium 
chloride  and  zinc  sulfide, 
(d)  tripod,  (e)  Bunsen 
burner. 


CHAPTER  IX 
THE  GERM  LIFE  OF  THE  SOIL 

Thus  far  we  have  been  engaged  in  considering  soil  as 
lifeless  material,  on  which  plants  are  to  be  grown,  but  which 
in  itself  is  inert  and  inanimate.  Such  a  conception  of  soil 
is  inadequate,  for  there  is  to  be  found  in  all  arable  land  a 
vast  number  of  forms  of  microscopic  life  that  really  consti- 
tute a  part  of  the  soil  itself.  From  the  standpoint  of  crop 
production  they  are  of  great  importance,  as  we  probably 
should  not  be  able  to  maintain  soil  fertility  without  them. 

Under  germ  life;  as  used  in  this  chapter,  are  included 
bacteria,  fungi,  alga?,  and  some  of  the  molds,  but  we  shall  in 
the  main,  dispense  with  these  distinctions  and  use  the  term 
"  germs  "  or  "  microorganisms  "  to  cover  all  or  any  of  them. 
In  spite  of  what  has  just  been  said  about  the  importance  of 
germs  in  plant  production,  there  are  many  that  are  injurious 
to  plants  both  directly  in  the  causation  of  disease,  or  indi- 
rectly by  contributing  to  processes  in  soils  that  are  detri- 
mental to  the  conditions  favorable  to  plant  growth.  In  dis- 
cussing the  subject  it  will  be  convenient  to  take  up  first 
the  soil  germs  that  are  directly  injurious  to  plants.  After 
that  the  subject  will  be  discussed  according  to  the  processes 
in  the  soil  with  which  microorganisms  are  concerned. 

154.  Microorganisms  injurious  to  crops.  —  The  soil  germs 
that  injure  crops  do  so  by  attacking  the  roots.  Those  that 
attack  other  parts  of  plants  may  live  in  the  soil  during  their 
spore  stage  but  they  are  not  strictly  microorganisms  of  the 
soil.     Some  of  the  more  common  diseases  produced  by  soil 

125 


126  SOILS   AND   FERTILIZERS 

germs  are  :  wilt  of  cotton,  cowpeas,  watermelon,  flax,  tobacco, 
tomatoes,  and  other  plants ;  damping-off  of  a  large  number 
of  plants,  root-rot  and  galls. 

Some  of  the  germs  causing  these  diseases  may  live  in  the 
soil  for  many  years.  Some  of  them  will  die  within  a  few 
years  if  the  plants  on  whose  roots  they  live  are  not  grown  on 
the  soil,  but  others  are  able  to  maintain  existence  on  almost 
any  organic  substance.  Infection  is  carried  in  the  soil,  or  by 
the  roots  of  the  plants  themselves,  consequently  farm  imple- 
ments or  manure  may  often  be  a  means  of  spreading  the  germs. 

For  combating  the  difficulties  caused  by  the  germs,  many 
methods  have  been  tried  with  more  or  less  success.  Rota- 
tion of  crops  is  successful  in  some  cases,  but  in  others  entire 
discontinuance  is  the  only  remedy.  The  use  of  lime  has  been 
beneficial  in  the  case  of  some  diseases.  Steam  sterilization 
for  greenhouse  soils  will  hold  in  check  a  considerable  number 
of  diseases.  Strains  of  cowpeas  and  cotton  plants  have  been 
bred  that  are  immune  to  the  effects  produced  by  some  germs. 

155.  Germs  not  directly  injurious  to  crops.  —  The  part 
played  by  the  microorganisms  that  affect  the  growth  of 
crops  may  be  roughly  listed  as  follows  :  (1)  action  on  mineral 
matter;  (2)  decomposition  of  non-nitrogenous  organic 
matter;  (3)  decomposition  of  nitrogenous  organic  matter; 
(4)  fixation  of  nitrogen  from  the  air  and  its  incorporation 
in  the  soil.  Most  of  the  processes  involved  in  these  trans- 
formations bring  about  conditions  favorable  to  crop  growth, 
but  some  of  them  are  injurious,  as,  for  instance,  the  forma- 
tion of  substances  poisonous  to  plants  and  the  liberation 
of  nitrogen  which  escapes  into  the  air.  These  injuries  are, 
however,  not  direct  effects  of  the  germs  on  the  crops,  but 
indirect  ones  caused  by  the  products  of  the  organisms. 

Bacteria,  fungi,  algae  and  certain  molds  all  play  a  part 
in  these  processes,  but  none  of  them  so  actively  as  do  the 
bacteria.     On  account  of  the  dominant  part  that  bacteria 


THE   GERM   LIFE   OF   THE  SOIL 


127 


take  in  soil  fertility  some  further  description  of  their  oc- 
currence in  soils  will  be  given. 

156.  Numbers  of  bacteria  in  soils.  —  It  is  naturally  to 
be  expected  that  soils  differ  greatly  in  the  number  of  bac- 
teria that  they  possess.  Where  there  is  a  large  amount  of 
easily  decomposable  organic  matter,-  the  number  is  great, 
and  consequently  in  rich  garden  soils  that  have  been  heavily 
manured,  or  where  the  carcasses  of  animals  have  been  buried 
the  bacterial  flora  is  dense.  On  the  other  hand,  in  very 
sandy  soils,  desert  soils  and  water-logged  soils,  bacteria  are 
few  in  number. 

While  there  are  usually  many  bacteria  in  fertile  soil,  it  is 
not  always  the  case  that  there  are  more  in  such  soils  than 
in  less  productive  ones.  The  number  of  bacteria  that  a 
soil  may  contain  cannot  be  considered  a  measure  of  its  pro- 
ductiveness. The  numbers  of  bacteria  found  in  one  gram 
of  soil  of  different  kinds  and  treated  in  different  ways  are 
given  in  the  following  table : 


Table  29. 


-Number  op  Bacteria  to  a  Gram  op  Soil  During 
Some  Period  of  the  Growing  Season 


Soil 

Depth 

Crop 

Number  op 
Bacteria 

Stiff  clay     .... 

3  inches 

Orchard     in     high 
state   of   cultiva- 
tion.    In      cover 

2,200,000 

Adjoining  soil  above 
and  of  same  char- 

3 inches 

crops 
Meadow  for  twelve 
years 

450,000 

acter 

Of     same     type     as 

above       .... 

Same  type  as  above 

3  inches 

Vegetables  and 
heavily  manured 

Scarlet      clover 
plowed  under  and 
alternated      with 
maize  for  ten  years 

1,800,000 
3,360,000 

128 


SOILS   AND   FERTILIZERS 


157.  Conditions  affecting  bacterial  growth.  —  The  en- 
vironment is  a  controlling  influence  in  the  development  of 
bacteria  as  it  is  of  all  organisms.  Among  the  important 
environmental  influences  are  the  supply  of  air  and  moisture, 
the  temperature,  the  presence  of  organic  matter,  and  the 

presence    or   absence    of 
acidity  in  the  soil. 

158.  Air  supply.  — 
While  all  bacteria  require 
some  air  for  their  growth, 
certain  of  them  are  able 
to  get  along  with  much 
less  than  others.  Those 
requiring  an  abundant 
supply  of  air  have  been 
called  aerobic  bacteria 
and  those  that  thrive 
better  on  a  small  air  sup- 
ply are  termed  anaerobic. 
The  bacteria  that  are  of 
the  greatest  benefit  to  the  soil  are,  in  the  main,  aerobes,  and 
those  that  are  injurious  in  their  action  are  chiefly  anaerobes. 
Bacteria,  however,  have  more  or  less  ability  to  adapt  them- 
selves to  a  larger  or  smaller  air  supply.  The  fact  that  struc- 
ture, texture  and  drainage  are  so  largely  instrumental  in 
regulating  the  quantity  of  air  in  the  soil  makes  them  im- 
portant factors  in  determining  the  kinds  of  bacterial  processes 
that  take  place  in  a  soil. 

159.  Moisture.  —  Like  other  forms  of  plant  life,  bacteria 
require  moisture  for  their  growth.  A  soil  may  become  so 
dry  that  the  number  of  bacteria  is  decreased,  but  owing  to 
their  rapid  multiplication  the  number  soon  increases  with 
a  replenished  moisture  supply.  An  excess  of  water  may 
decrease  the  number  or  change  the  character  of  the  flora 


C 


Fig.  23.  —  Diagram  showing  the  relative 
sizes  of  bacteria  and  some  soil  particles. 
(A)  a  fine  sand  particle,  (B)  a  large  clay 
particle,  (C)  a  few  soil  bacteria.  All  are 
magnified  at  the  same  rate. 


THE   GERM   LIFE  OF   THE  SOIL  129 

by  cutting  off  the  air  supply.  A  well-drained  soil  in  good 
tilth  affords  the  best  moisture  conditions  for  the  develop- 
ment of  desirable  bacteria. 

160.  Temperature.  —  It  is  seldom  that  soil  temperatures 
become  sufficiently  high  to  interfere  with  bacterial  activity, 
and  then  it  is  only  near  the  surface.  Freezing  does  not 
kill  most  soil  bacteria,  but  it  renders  them  inactive  during 
the  frozen  period.  It  is  in  the  early  spring  that  temperature 
is  an  important  factor  so  far  as  its  effect  on  bacteria  is  con- 
cerned. At  that  season  it  is  desirable  to  warm  the  soil 
as  rapidly  as  possible. 

161.  Organic  matter.  —  Many  forms  of  bacteria  utilize 
the  organic  matter  of  the  soil  as  a  source  of  food  supply. 
Others  thrive  without  any  organic  matter.  For  the  proper 
functioning  of  a  normal  bacterial  flora  there  should  be  a 
good  supply  of  organic  matter  in  the  soil. 

162.  Soil  acidity.  —  Most  of  the  useful  bacteria  make 
their  best  growth  in  a  soil  that  shows  no  acidity.  This  is 
notably  true  of  those  bacteria  that  assist  in  the  process 
of  making  organic  nitrogenous  matter  suitable  for  use  by 
plants,  and  also  the  symbiotic  bacteria  of  alfalfa  and  red 
clover.  One  of  the  important  effects  of  lime  is  the  increased 
activity  of  beneficial  soil  bacteria. 

163.  Bacteria  in  relation  to  soil  fertility.  —  We  have  now 
discussed  the  conditions  under  which  soil  bacteria  grow. 
The  next  step  will  be  to  describe  the  various  processes  by 
which  they  increase  soil  fertility  and  also,  to  some  extent, 
by  which  they  unfavorably  influence  soil  productiveness.  To 
do  this  they  will  be  discussed  in  the  order  stated  in  §  155. 
The  reader  must,  however,  bear  in  mind  that  there  are  doubt- 
less many  bacteriological  processes  in  the  soil  regarding 
which  nothing  is  known. 

164.  Action  on  mineral  matter.  —  There  are,  without 
doubt,  microorganisms  that  act  on  mineral  matter  in  soil, 

K 


130  SOILS   AND   FERTILIZERS 

attacking  the  insoluble  substances  and  rendering  them  more 
soluble.  The  phase  of  this  subject  that  is  of  most  apparent 
agricultural  importance  is  the  effect  of  microorganisms 
on  the  very  difficultly  soluble  rock  or  bone  phosphoric  acid, 
converting  it  into  phosphoric  acid  available  to  plants. 
In  laboratory  experiments  with  pure  cultures  of  bacteria 
these  changes  have  been  found  to  occur.  There  has  also 
been  found  to  take  place  a  reverse  process  by  which  the  more 
easily  soluble  phosphoric  acid  is  converted  into  the  less 
soluble  one.  There  is,  at  present,  no  way  by  which  man  can 
control  this  operation  in  the  soil.  It  has  been  held  that  the 
presence  of  a  large  quantity  of  organic  matter  will  make  the 
phosphoric  acid  of  rock  readily  available.  The  results  of 
experiments  with  raw  rock  phosphate  and  farm  manure  do 
not  always  confirm  this  idea.  Under  some  conditions  the 
dominant  process  may  be  the  conversion  of  difficultly  soluble 
into  readily  soluble  phosphoric  acid,  while  under  other 
conditions  the  reverse  may  take  place. 

165.  Decomposition  of  non-nitrogenous  organic  matter. 
—  There  is  much  organic  matter  on  the  surface  or  in  the 
plowed  soil  that  contains  no  nitrogen.  The  cell  walls  of 
plants,  and  the  sugars,  starch  and  fats  of  plants  contain  no 
nitrogen.  These  substances  are  broken  down  by  bacteria, 
passing  through  different  stages  among  which  acids  occur, 
and  finally  being  resolved  into  carbon  dioxide  and  water. 
We  have  seen  that  the  plant  uses  carbon  dioxide  as  food 
material,  and  we  may  now  understand  the  cycle  through 
which  the  carbon  of  this  gas  goes.  Plants  absorb  carbon 
dioxide  through  their  leaves,  decompose  it  and  use  the  carbon 
in  their  tissues.  After  the  plant  is  dead,  the  tissues  decom- 
pose and  carbon  dioxide  is  again  formed  and  passes  into  the 
air.  Just  as  higher  plants  live  and  grow  by  using  carbon 
from  carbon  dioxide,  so  bacteria  live  and  grow  by  using  the 
carbon  of  plant  tissues. 


THE   GERM   LIFE   OF   THE  SOIL 


131 


166.  Decomposition  of  nitrogenous  organic  matter.  — 
The  main  difference  between  the  decomposition  of  non- 
nitrogenous  and  nitrogenous  organic  matter  is  that  in  the 
latter  nitrogen  and  usually  sulfur  play  a  part.  The  sulfur 
is  not  of  so  much  importance,  but  it  is  very  necessary  that 
we  should  follow  the  various  processes  through  which  nitro- 
gen is  transformed  from  organic  substances  into  the  final 
forms  in  which  it  is  again  used  by  plants  or  returned  to  the 
air.     These  processes  will  be  treated  under  the  following 


A  5  C  D 

Fig.  24.  —  Appearance  of  some  soil  germs  under  the  microscope.  (A)  free 
living  nitrogen-fixing  bacteria  (Azotobacter) ,  (B)  bacteria  that  cause  one 
step  in  the  production  of  nitrates  from  ammonia  (Nitrosomonas),  (C)  nitro- 
gen-fixing bacteria  from  the  nodules  of  leguminous  plants  (Radicicola), 
(D)  ammonia-forming  bacteria  (Proteus  vulgaris). 

heads  :     (1)  ammonification ;    (2)  nitrification ;    (3)  denitri- 
fication. 

Organic  nitrogenous  matter  when  it  first  enters  the  soil 
as  plant  or  animal  remains  or  as  solid  farm  manure  or  green- 
manure  is  largely  in  the  form  of  what  are  known  as  proteids. 
As  soon  as  such  material  is  incorporated  in  any  normal 
soil,  decomposition  begins  and  the  rate  at  which  it  proceeds 
depends  on  the  character  of  the  soil  in  which  the  process 
is  going  on.  There  are  several  different  forms  of  bac- 
teria that  are  capable  of  decomposing  proteins  and  there 
are  always  enough  of  these  in  any  arable  soil  to  do  the  work 
if  the  soil  has  the  proper  moisture,  ventilation  and  heat  and 
is  not  acid. 


132  SOILS   AND   FERTILIZERS 

167.  Ammonification.  —  Various  intermediate  products 
occur  in  the  breaking  down  of  proteids,  but  we  are  concerned 
chiefly  with  the  product  known  as  ammonia.  This  is  the 
nitrogenous  substance  contained  in  many  fertilizers,  and 
it  may  be  used  by  some  crops  directly  as  food  material. 
Rice,  for  instance,  and  probably  other  swamp  plants  can 
use  ammonia  better  than  any  other  form  of  nitrogen.  Even 
some  upland  crops  like  corn,  peas,  barley  and  potatoes  can 
use  it,  but  not  as  well  as  they  can  the  form  of  nitrogen  into 
which  ammonia  is  transformed  by  the  next  fermentation, 
namely  nitrification. 

It  may  be  well  to  say,  in  passing,  that  there  are  some  other 
products  intermediate  between  proteids  and  ammonia  that 
are  directly  used  by  plants,  and  it  is  altogether  likely  that 
farm  manure  owes  part  of  its  great  fertilizing  value  to  some 
of  these  substances  that  it  may  possess. 

168.  Nitrification.  —  This  is  the  final  step  in  the  prepara- 
tion of  nitrogen  for  use  by  most  agricultural  plants,  for  it  is 
in  the  form  produced  by  nitrification  that  nitrogen  is  most 
useful  to  most  crops.  This  form  is  called  nitrates.  Like 
ammonification  this  fermentation  goes  on  in  any  normal 
soil  if  the  ammonia  is  there  for  it  to  work  on,  and  also  like 
ammonification  the  conditions  of  temperature,  air  supply, 
moisture  and  lime  must  be  satisfactory  or  the  process  will 
be  so  slow  that  plants  will  suffer  for  nitrogen. 

There  has  been  some  question  as  to  whether  heavy  manur- 
ing with  organic  manures  results  in  a  decreased  nitrification. 
While  this  may  be  the  case  where  farm  manure  is  used  in 
very  heavy  dressings  of  as  high  as  fifty  to  a  hundred  tons 
to  the  acre,  as  is  sometimes  done  in  truck  crop  gardening, 
it  is  not  likely  to  be  the  case  in  soils  in  which  ordinary  field 
crops  are  grown. 

169.  Effect  of  soil  aeration  on  nitrate  formation.  —  One  of 
the  most  important  conditions  that  must  obtain,  if  ammon- 


THE   GERM   LIFE   OF    THE   SOIL 


133 


ification  and  nitrification  are  to  proceed  rapidly,  is  an  ade- 
quate supply  of  air  in  the  soil  and  this  can  only  be  secured 
by  thorough  tillage.  This  is  illustrated  by  an  experiment 
in  which  columns  of  soil  eight  inches  in  diameter  and  eight 
inches  high  were  removed  from  a  field  of  clay  loam  and  car- 
ried to  the  greenhouse  without  disturbing  the  structure  of 
the  soil  as  it  existed  in  the  field.  At  the  same  time  vessels 
of  similar  size  were  filled  with  soil  dug  from  a  spot  near  by. 
These  represented  unaerated  and  aerated  soils  respectively, 
because  one  had  been  undisturbed,  while  the  .other  had 
been  thoroughly  exposed  to  the  air.  Both  were  kept  at  the 
same  temperature  and  moisture  content  in  the  greenhouse 
but  no  plants  were  grown  in  them.  The  production  of 
nitrates  was  as  follows : 


Table   30. 


Formation   of  Nitrates   in  Unaerated   and   in 
Aerated  Soil 


Times  of  Making  Analyses 

Nitrates  in  Dry  Soil,  Parts  per 
Million 

Unaerated  soil 

Aerated  soil 

When  taken  from  field      .... 
After  standing  one  month      .     .     . 
After  standing  two  months         .     . 

3.2 
4.2 
9.0 

3.2 
17.6 
45.6 

170.  Effect  of  temperature  on  nitrate  formation.  —  There 
is  a  considerable  range  of  temperature  through  which  the 
process  of  nitrate  formation  proceeds  with  more  or  less 
intensity.  Freezing  stops  the  fermentation,  but  does  not 
kill  the  bacteria,  whose  activity  is  resumed  when  the  tempera- 
ture rises  to  about  40°  F.  and  increases  until  a  temperature 
approaching  75°  to  85°  F.  is  reached,  after  which  the  in- 
tensity gradually  diminishes.  At  110°  F.  and  above,  there 
is  little  formation  of  nitrates. 


134 


SOILS   AND   FERTILIZERS 


The  more  rapidly  a  soil  becomes  warm  in  the  spring,  the 
sooner  will  nitrates  be  formed.  Crops  like  winter  wheat 
will  often  begin  growth  before  the  soil  is  sufficiently  warm 
to  admit  of  the  rapid  formation  of  nitrates  and,  as  winter 
rains  will  have  leached  from  the  soil  nitrates  that  accumu- 
lated during  the  preceding  year,  the  plants  often  suffer 
seriously  from  lack  of  nitrogen. 

It  is  not  often  that  the  soil  for  several  inches  below 
the  surface  becomes  hot  enough,  even  in  midsummer,  to 
interfere  with  nitrate  formation.  Crops  that  make  their 
growth  in  late  spring  or  summer  are  not  likely  to  suffer 
for  nitrates  unless  the  total  supply  of  nitrogen  is  deficient. 

171.  Effect  of  sod  on  nitrate  formation.  —  In  soil  on 
which  there  is  a  good  stand  of  grass  very  little  nitrate  is 
ever  found.  Sod  apparently  has  a  depressing  influence  on 
nitrate  formation.  On  the  same  type  of  soil  as  that  used  in 
the  experiment  last  described,  the  average  quantities  of 
nitrates  for  each  month  of  the  growing  season  in  the  surface 
eight  inches  of  sod  land,  as  compared  with  corn  land  under 
the  same  manuring,  were  as  follows  : 

Table  31.  —  Nitrates   in  Soil  Under  Sod  and  Under  Corn 


There  was  more  nitrogen  contained  in  the  corn  crop  than 
there  was  in  the  timothy  crop,  so  that  the  larger  quantity 


THE   GERM   LIFE   OF   THE  SOIL  135 

of  nitrates  in  the  corn  land  cannot  be  attributed  to  failure 
of  the  plants  to  remove  it.  Grass  appears  to  have  a  decidedly 
depressing  effect  on  the  process  of  nitrate  formation,  and 
this  may  be  one  reason  why  grass  is  generally  a  detriment 
to  the  growth  of  young  orchards. 

172.  Depths  at  which  nitrate  formation  takes  place.  — 
It  is  probable  that  the  processes  by  which  nitrates  are  formed 
are,  in  humid  regions,  confined  largely  to  the  furrow  slice 
of  soil.  Nitrates  found  below  that  point  have  probably 
been,  in  large  measure,  washed  down  from  above.  The  sub- 
soil in  such  a  region  is  not  a  verjr  favorable  medium  for  these 
processes.  In  arid  and  semi-arid  regions,  however,  the  case 
is  different.  Here  the  distinction  between  surface  soil  and 
subsoil  is  not  so  marked,  and  owing  to  the  rich  and  porous 
nature  of  these  subsoils  nitrification  may  proceed  at  con- 
siderable depths. 

173.  Loss  of  nitrates  in  drainage.  —  It  has  already  been 
shown  that  there  is  a  large  removal  of  nitrates  in  drainage 
water  (§  121).  As  nitrogen  is  the  most  expensive  of  fer- 
tilizer constituents  every  effort  should  be  made  to  prevent 
this  loss.  A  very  effective  way  to  do  so  is  to  have  a  crop 
growing  on  the  land  during  all  of  the  growing  season.  A 
comparison  of  the  loss  from  the  planted  and  unplanted  soil, 
in  the  paragraph  referred  to,  will  show  how  effective  a  crop 
is  as  a  means  of  preventing  loss  of  nitrates  in  drainage 
water. 

Hall  states  that  nitrates  formed  during  the  summer  or 
the  autumn  of  one  year  are  practically  all  removed  from  the 
soil  of  the  Rothamsted  fields  before  the  crops  of  the  following 
year  have  advanced  sufficiently  to  use  them. 

174.  Denitrification.  —  After  nitrates  have  been  formed 
by  the  processes  that  have  just  been  described,  there  are 
other  bacteria  or  some  of  the  same  bacteria  acting  under 
different  conditions  that  attack  the  nitrates  and  convert 


136  SOILS   AND   FERTILIZERS 

them  into  other  substances.  There  are  three  different  pro- 
cesses and  three  distinct  products  that  may  result.  These 
are :  (1)  reduction  of  nitrates  to  ammonia ;  (2)  reduction 
of  nitrates  to  free  nitrogen ;  (3)  conversion  of  nitrates  into 
organic  nitrogenous  substances.  All  of  these  fermentations 
result  in  a  conversion  of  the  more  easily  available  forms  of 
nitrogen  into  less  available,  and  in  the  case  of  the  production 
of  free  nitrogen  there  is  a  loss  of  nitrogen  from  the  soil,  as 
the  free  nitrogen  is  a  gas  and  passes  off  into  the  air. 

Most  of  the  bacteria  that  effect  these  changes  do  so  only 
when  there  is  a  limited  supply  of  air,  so  that  a  thorough  aera- 
tion of  the  soil  practically  prevents  denitrification.  Straw 
apparently  induces  denitrification  when  conditions  are  at 
all  favorable  for  that  process. 

The  addition  of  a  nitrate  fertilizer  to  a  well-drained  soil 
receiving  farm  manure  is  not  likely  to  result  in  a  loss  of 
nitrates  unless  the  dressing  of  manure  has  been  extremely 
heavy.  At  the  Rothamsted  Experiment  Station,  where 
large  quantities  of  nitrate  of  soda  are  used  every  year  in 
connections  with  annual  dressings  of  farm  manure,  the  nitrate 
produces  nearly  as  large  an  increase  when  applied  to  the 
manured  as  when  added  to  the  unmanured  plat. 

Very  heavy  applications  of  farm  manure,  of  fifty  tons  to 
the  acre  or  more,  may  temporarily  interfere  with  formation 
of  nitrates.  The  plowing  under  of  large  quantities  of  straw 
and  even,  under  some  conditions,  green-manures  may  have 
this  effect. 

175.  Nitrogen  fixation.  —  Another  and  very  important 
bacteriological  process  is  the  transfer  of  nitrogen  from  the 
atmosphere  to  the  soil.  This  process  is  termed  "  nitrogen 
fixation  "  and  it  may  occur  either  with  the  assistance  of  higher 
plants,  or  without.  The  first  of  these  is  called  nitrogen 
fixation  through  symbiosis  with  higher  plants,  the  second 
nitrogen  fixation  by  soil  organisms  not  associated  with  plants. 


THE   GERM   LIFE   OF   THE  SOIL  137 

The  importance  of  this  process  to  soil  productiveness  may 
be  realized  when  it  is  considered  that  nitrogen  is  the  most 
expensive  of  all  the  ingredients  of  commercial  fertilizers, 
and  that  many  pounds  to  the  acre  may  be  secured  by  en- 
couraging the  growth  of  the  bacteria  concerned  in  the  op- 
eration. 

176.  Nitrogen  fixation  through  symbiosis  with  higher 
plants.  —  The  value  of  certain  plants  as  soil  improvers  has 
long  been  recognized,  and  within  the  last  half  century  their 
ability  to  improve  soil  has  been  traced  to  their  property  of 
taking  nitrogen  from  the  air  and  leaving  it  in  the  soil.  The 
plants  that  do  this  belong,  with  a  few  exceptions,  to  the 
family  of  legumes. 

The  method  by  which  nitrogen  is  transferred  from  the  air 
to  the  soil  is  not  perfectly  understood,  but  it  appears  to 
be  somewhat  as  follows  : 

On  the  roots  of  leguminous  plants  are  found  nodules  or 
tubercles,  which  are  large  enough  to  be  seen  with  the  naked 
eye,  and  in  which  live  the  bacteria  that  remove  the  nitrogen 
from  the  soil  air  and  convert  it  into  nitrogenous  organic 
matter,  that  then  becomes  a  part  of  the  host  plant.  As  a 
consequence  legumes  are  very  rich  in  nitrogen,  and  the 
tubercles  contain  an  especially  large  quantity.  When  the 
roots  and  nodules  decay  and  when  the  aboveground  part  of 
the  plant  is  plowed  under,  the  nitrogenous  matter  they  con- 
tain becomes  a  part  of  the  soil. 

If  the  nitrogen-fixing  bacteria  are  not  present  in  the  soil 
or  other  medium  in  which  the  legumes  grow,  no  nodules 
will  be  formed  and  no  atmospheric  nitrogen  will  be  fixed. 
The  plant  must  then  live  on  the  combined  nitrogen  of  the 
soil  just  as  other  plants  do  and  consequently  it  does  not 
serve  to  increase  the  store  of  soil  nitrogen.  In  fact,  the 
reverse  occurs,  for  on  account  of  the  high  nitrogen  content 
of  legumes,  they  withdraw,  under  these  conditions,  large 


138  SOILS   AND   FERTILIZERS 

quantities  of  nitrogen  from  the  soil.  Even  when  the  nitro- 
gen-fixing bacteria  are  present,  leguminous  plants  maj'  draw 
much  of  their  nitrogen  from  the  nitrates  in  a  soil  that  is 
rich  in  these  substances.  As  a  result,  less  nitrogen  is  taken 
from  the  air  and  if  the  crop  is  removed  the  quantity  of  nitro- 
gen remaining  in  the  soil  may  be  no  greater  than  before  the 
legume  was  planted. 

177.  Soil  inoculation  for  legumes.  —  After  it  had  been 
discovered  that  leguminous  plants  acted  as  hosts  for  bacteria 
that  draw  nitrogen  from  the  soil  air,  the  idea  at  once  pre- 
sented itself  that  soils  not  containing  these  bacteria  could  be 
inoculated  with  them,  and  thus  be  made  much  more  suitable 
to  the  growth  of  legumes.  It  has  been  found  to  be  practi- 
cable to  accomplish  this  inoculation  by  spreading  on  the  land 
soil  from  a  field  on  which  the  kind  of  legume  it  is  proposed 
to  plant  has  grown  successfully.  The  fact  that  inoculation 
by  means  of  soil  from  other  fields  may  possibly  transmit 
weed  seeds  and  fungous  diseases,  and  that  it  also  necessitates 
the  transportation  of  a  great  bulk  and  weight  of  material  has 
led  to  numerous  efforts  to  inoculate  soil  by  means  of  pure 
cultures  of  bacteria.  This  has  been  fairly  successful  in  re- 
cent years,  but  the  surest  way  is  by  the  use  of  soil.  However, 
pure  cultures  may  be  obtained  from  most  of  the  agricultural 
experiment  stations  and  from  the  U.  S.  Department  of  Agri- 
culture, Washington,  D.  C. 

It  must  be  borne  in  mind  that  when  soil  is  used  for  inocula- 
tion it  must  come  from  a  field  that  has  produced  a  good  crop 
of  the  same  kind  of  legume  that  is  to  be  planted  on  the  inoc- 
ulated field,  also  that  the  soil  must  not  be  allowed  to  become 
very  dry,  as  that  is  likely  to  kill  the  bacteria.  The  inoculat- 
ing soil  is  applied  after  plowing  and  is  harrowed  in. 

If  inoculation  is  to  be  successful,  the  soil  on  which  the 
legume  is  to  be  planted  must  be  of  a  nature  favorable  to  the 
legume,  otherwise  growth  will  not  be  normal  in  spite  of 


THE   GERM   LIFE   OF    THE  SOIL 


139 


inoculation.  The  conditions  favorable  for  legumes  are  the 
same  as  for  most  upland  crops,  namely  good  drainage  and 
good  tilth,  while  for  red  clover,  peas  or  alfalfa  the  soil  should 
have  an  abundant  supply  of  lime. 

Not  only  is  the  yield  of  an  alfalfa  crop  greatly  increased 
by  the  presence  of  the  nitrogen-fixing  organisms  and  also 


Nitrogen  of  air 


$b  animal 


r#EE  F/XAJjO/i 
Free  m'fi 


troden  Comdex.  compou/M, 

DiWTRIFICATIOn '.-•  ;. 


WTRIFICATICM 


0/4 

ri  _ 


decay..- y 

-  inTERMEDlATC  PfZODUCTi 
Carbon  dioxide,  etc 


4M/10MA 


Fig.  25.  —  The  cycle  through  which  nitrogen  passes  in  its  movements 
among  soil,  plant,  animal  and  atmosphere.  Solid  lines  in  the  diagram  indi- 
cate the  usual  transformations  of  nitrogen.  Dotted  lines  indicate  the  occa- 
sional transformations. 


of  lime,  but  the  percentage  of  nitrogen  that  the  crop  contains 
is  thereby  increased. 

178.  Nitrogen  fixation  by  free  living  germs.  —  In  addi- 
tion to  the  nitrogen-fixing  bacteria  described  above,  there 
exist  in  many  soils  germs  that  are  able  to  take  nitrogen  from 
the  atmosphere  and  convert  it  into  nitrogenous  organic  mat- 
ter without  the  aid  of  a  host  plant.  How  extensively  these 
organisms  operate  is  difficult  to  say.  In  poor  land  they  are 
often  effective  in  recouping  the  supply  of  soil  nitrogen,  but 
it  is  doubtful  to  what  extent  they  function  in  rich  soil.  At 
the  Rothamsted  Experiment  Station  one  of  the  fields  had 
been  allowed  to  lie  unused  for  many  years  because  it  was  too 


140  SOILS   AND    FERTILIZERS 

poor  to  cultivate.  It  grew  up  mainly  to  grass,  with  a  very 
few  legumes,  and  in  the  course  of  twenty  years  it  had  gained 
nitrogen  at  the  rate  of  twenty-five  pounds  to  the  acre  an- 
nually. With  the  exception  of  about  five  pounds  to  the  acre 
that  was  brought  down  by  rain,  dust  and  the  like,  the  accu- 
mulation was  doubtless  due  to  the  free-living  germs. 

QUESTIONS 

1.  Explain  the  difference  between  the  directly  injurious  and  the 
indirectly  injurious  effect  of  soil  germs  on  plant  growth. 

2.  Are  the  numbers  of  bacteria  in  soils  rather  uniform,  or  do 
they  vary  greatly  in  different  soils  ? 

3.  Describe  the  relation  of  soil  bacteria  to  the  air  supply. 

4.  Their  relation  to  moisture. 

5.  Their  relation  to  temperature. 

6.  Their  relation  to  organic  matter. 

7.  Their  relation  to  soil  acidity. 

8.  Their  relation  to  soil  fertility. 

9.  Describe  the  cycle  through  which  carbon  passes  from  plant 
to  soil  and  back  to  air  again. 

10.  Explain  the  fermentation  known  as  ammonification. 

11.  Describe  what  is  meant  by  nitrification. 

12.  How  do  soils  of  arid  and  humid  regions  differ  in  respect  to 
the  depths  at  which  nitrate  formation  occurs  ? 

13.  Why  does  nitrate  formation  not  take  place  in  early  spring  ? 

14.  Describe  three  fermentations  by  which  the  nitrogen  of  ni- 
trates is  converted  into  other  forms. 

15.  Describe  the  two  processes  by  which  atmospheric  nitrogen 
is  fixed  in  the  soil  by  germs. 

16.  Describe  the  cycle  through  which  nitrogen  passes  from  the 
plant  to  soil  and  back  to  plant  again. 

LABORATORY    EXERCISES 

Exercise  I.  —  Test  for  nitrates  in  soil. 

Materials.  —  A  rich  garden  loam,  a  500  c.c.  vessel  for  mixing 
the  soil  and  water,  wooden  stirrer,  funnel  and  filter  paper,  hydrate 
of  lime,  water  bath,  ammonium  hydrate  solution,  evaporating  dish, 
phenoldisulphonic  acid. 


THE   GERM   LIFE   OF    THE  SOIL  141 

The  phenoldisulphonic  acid  is  prepared  as  follows :  To  37  grams 
of  concentrated  sulphuric  acid  add  3  grams  of  pure  crystalline  phenol. 
Heat  for  six  hours  in  a  lightly  stoppered  flask  set  in  boiling  water. 

Procedure.  —  To  50  grams  of  soil  in  the  500  c.c.  container  add 
250  c.c.  of  distilled  water.  Add  1  gram  of  hydrate  of  lime  to  floccu- 
late the  soiL  Stir  three  minutes  and  allow  to  stand  20  minutes. 
Pipette  off  25  or  30  c.c.  of  the  clear  supernatant  liquid  and  filter  it. 
Evaporate  10  c.c.  of  the  filtrate  to  dryness  over  a  water  bath  in  an 
evaporating  dish.  Moisten  with  a  few  drops  of  phenoldisulphonic 
acid  and  stir  well.  Allow  to  stand  a  few  minutes.  Dilute  with  a 
few  cubic  centimeters  of  water  and  neutralize  with  ammonia.  The 
development  of  a  yellow  color  is  an  indication  of  the  presence  of 
nitrates  and  its  intensity  is  a  measure  of  the  amount. 

Exercise  II.  —  Test  for  ammonia  in  soil. 

Materials.  —  A  small  portion  of  the  soil  solution  obtained  in 
Exercise  I,  and  Nessler's  solution. 

The  Nessler's  solution  is  made  as  follows  :  To  a  250  c.c. 
solution  of  potassium  iodide  (made  by  dissolving  63  grams  in  250 
c.c.  of  ammonia-free  water)  add  a  saturated  solution  of  mercuric 
chloride  until  the  precipitate  nearly  all  redissolves.  Now  add  250 
c.c.  of  a  solution  of  potassium  hydrate  (150  grams  to  250  c.c.  of 
water).  Make  up  the  whole  solution  to  one  liter.  Allow  to  stand 
until  any  precipitate  has  settled  before  using.  Keep  in  well-stop- 
pered bottle  in  the  dark. 

Procedure.  —  To  ten  cubic  centimeters  of  the  soil  extract  add  a 
few  cubic  centimeters  of  Nessler's  solution.  The  development  of  a 
light  yellow  is  an  indication  of  ammonia. 

Exercise  III.  —  Factors  affecting  nitrification. 

Materials.  —  Same  as  Exercise  I  plus  four  100  c.c.  graduated  cyl- 
inders.    Use  moist  acid  soil  from  beneath  sod. 

Procedure.  —  Place  four  50-gram  portions  of  a  moist  soil  from 
beneath  sod  in  8-ounce  wide-mouth  bottles.  Bring  soil  of  bottle 
No.  1  to  optimum  moisture.  Saturate  soil  of  bottle  No.  2  to  give 
poor  aeration.  Thoroughly  mix  one  gram  of  carbonate  of  lime  to 
bottle  No.  3  and  one  gram  of  lime  plus  one-tenth  gram  of  ammonium 
sulfate  with  soil  of  bottle  No.  4.  Raise  both  to  optimum  moisture. 
Stopper  all  bottles  lightly  with  cotton  and  allow  to  stand  in  a  warm 
room  for  a  week  or  ten  days. 

Develop  nitrates  from  these  samples  as  directed  in  Exercise  I. 
Pour  developed  solutions  into  100  c.c.  graduates  and  dilute  to  a  con- 


142  SOILS   AND   FERTILIZERS 

venient  mark.  Compare  the  intensity  of  color  from  the  various 
treatments  and  explain  the  results  obtained.  How  may  the  results 
be  applied  to  field  practice  ? 

Exercise  IV.  —  Examination  of  legume  nodules. 

Visit  fields  of  red  clover, vetch,  alfalfa,  peas,  etc.,  and  with  a  spade 
carefully  uproot  some  of  the  plants  and  search  for  nodules.  Note 
the  number,  size  and  location  of  the  nodules  on  the  various  legumes. 
If  suitable  specimens  of  roots  bearing  nodules  are  found  it  might  be 
feasible  to  preserve  them  for  exhibition  purposes.  They  may  be 
satisfactorily  preserved  in  glass  cylinders  filled  with  water  to  which 
a  few  drops  of  formalin  have  been  added.  The  cylinders  should  be 
tightly  stoppered  to  prevent  evaporation. 

Exercise  V.  —  Examination  of  nodule  bacteria. 

If  the  instructor  has  an  oil  immersion  microscope  available,  with 
staining  mixtures  and  other  facilities  for  preparing  slides  of  bacteria, 
this  would  be  a  desirable  demonstration.  The  pupil  would  then 
gain  a  first  hand  knowledge  of  bacteria.  Other  soil  organisms  might 
also  be  mounted  for  class  use. 

Exercise  VI.  —  Soil  inoculation. 

If  the  instructor  could  arrange  in  some  way  to  cooperate  with  a 
near-by  farmer  in  inoculating  his  soil  by  some  of  the  means  available 
for  the  purpose,  this  would  be  a  valuable  demonstration  for  the  pupils 
to  attend.  Actually  seeing  a  thing  done  is  worth  much  more  than 
mere  class  room  study. 


CHAPTER  X 

SOIL  AIR  AND  SOIL   TEMPERATURE 

The  volume  of  soil  air  depends  on  the  volume  of  pore  space 
that  is  not  filled  with  water.  It  is,  therefore,  evident  that 
ordinarily  the  non-capillary  or  larger  spaces  are  the  ones 
that  contain  air.  It  will  be  remembered  that  the  most  im- 
portant conditions  that  favor  a  large  pore  space  in  soils  are : 
(1)  granular  structure,  (2)  presence  of  organic  matter.  In 
any  soil  the  pore  space  may  change  from  time  to  time  with 
the  structure  and  the  application  of  organic  matter. 

179.  Soil  air  contained  largely  in  non-capillary  spaces.  — 
The  removal  of  water  allows  more  space  to  be  filled  with 
air.  Immediately  after  a  heavy  rain  much  of  the  pore  space 
of  the  surface  soil  is  filled  with  water.  After  this  has  had 
time  to  drain  away  only  the  capillary  spaces  remain  filled, 
but  capillary  water  is  lost  much  more  slowly.  It  is  the  non- 
capillary  pore  space  that,  during  the  greater  part  of  the  time, 
constitutes  the  air  space  of  the  soil.  As  a  compact  condition 
of  soil  results  in  smaller  pore  spaces  and  consequently  in 
more  capillary  spaces,  it  causes  a  decrease  in  the  volume  of 
air. 

180.  There  may  be  too  much  or  too  little  soil  air.  —  Soil 
air  is  a  necessary  constituent  of  a  productive  soil,  as  will  be 
explained  later,  but  it  is  not  always  the  case  that  the  more 
air  space  in  a  soil  the  better  it  is  for  crop  production.  Very 
large  air  spaces,  like  those  found  in  a  cloddy  soil,  allow  the  soil 
to  dry  out  too  readily.     Up  to  a  certain  limit  a  good  supply 

143 


144  SOILS   AND   FERTILIZERS 

of  soil  air  is  desirable,  but  there  can  be  too  much.  On  the 
other  hand,  there  may  be  too  little.  It  may  be  assumed 
that  when  a  soil  is  in  a  compact  condition  it  has  an  insuffi- 
cient supply  of  air. 

181.  Movement  of  soil  air.  —  The  rate  at  which  air  moves 
through  a  soil  depends  largely  on  the  size  of  the  pore  spaces, 
rather  than  on  their  aggregate  volume.  Movement  of  air 
is  necessary  to  ventilate  the  soil,  just  as  it  is  to  freshen  the 
air  in  a  house  in  which  many  persons  live,  or  a  public  hall 
in  which  people  congregate.  Among  the  factors  concerned 
with  the  movement  of  soil  air  are  (1)  movement  of  water, 
(2)  diffusion  of  gases,  (3)  some  minor  conditions,  like  dif- 
ferences in  temperature  between  atmospheric  air  and  soil 
air,  periodic  changes  in  atmospheric  pressure  and  suction 
produced  by  wind. 

182.  Movement  of  water.  —  The  movement  of  soil  air 
caused  by  water  is  probably  the  most  important  of  any. 
When  rain  falls,  the  surface  soil  first  receives  the  water, 
which  usually  fills  all  of  the  spaces  between  the  particles. 
As  the  water  descends,  air  is  driven  from  the  pore  spaces 
to  make  room  for  the  water,  the  air  escaping  upward  as  the 
water  goes  downward,  or  else  being  forced  out  through  the 
drainage  channels  below.  The  movement  of  air  proceeds 
to  the  depth  of  the  water  table.  Fully  one-fourth  of  the 
air  in  a  soil  may  be  forced  out  by  a  normal- change  in  the 
moisture  content  of  a  soil.     As  the  soil  dries  out  air  returns. 

183.  Diffusion  of  gases.  —  Owing  to  the  difference  in  com- 
position between  the  atmospheric  air  and  soil  air,  there  is  a 
tendency  for  them  to  mix,  and  this  process  would  go  on  until 
the  two  had  the  same  composition,  were  it  not  for  the  fact 
that  gases  are  continually  being  formed  in  the  soil  and  thus 
prevent  the  soil  from  attaining  the  same  composition  as  the 
atmospheric  air.  The  process  of  diffusion  is,  therefore,  con- 
tinuous. 


SOIL   AIR  AND   SOIL    TEMPERATURE 


145 


The  rate  of  diffusion  depends  on  the  total  volume  of  the 
pore  spaces  and  not  on  their  average  size.  A  soil  in  good 
tilth  is  therefore  in  suitable  condition  for  permitting  dif- 
fusion of  atmospheric  and  soil  air. 

184.  Composition  of  soil  air.  —  The  greater  part  of  the 
soil  air,  like  atmospheric  air,  is  composed  of  nitrogen  and 
oxygen.  The  principal  difference  between  soil  air  and 
atmospheric  air,  in  respect  to  composition,  is  that  the  former 
contains  more  moisture  and  more  carbon  dioxide.  The 
moisture  comes  from  evaporation  of  water  in  the  soil. 
The  carbon  dioxide  is  produced  for  the  most  part  by  the 
germs  in  the  soil  and  by  roots.  The  following  table  shows 
how  soils  may  vary  in  their  content  of  carbon  dioxide. 


Table  32. 


Percentage  of  Carbon  Dioxide  in  Air  of  Differ- 
ent Soils  at  Same  Depth 


Character  of  Soil 


Percentage  Composition 


Carbon 
Dioxide 


Oxygen 


Nitrogen 


Forest  soil . 

Clay  soil 

Asparagus  bed  not  manured  for  one 

year        

Asparagus  bed  freshly  manured  .  . 
Sandy  soil  six  days  after  manuring  . 
Vegetable  mold  compost 


0.87 
0.66 


0.74 
1.54 
2.21 
3.64 


19.61 
19.99 

19.02 

18.80 

16.45 


79.52 
79.35 

80.24 
79.66 

79.91 


Soils  that  are  high  in  organic  matter  and  in  which  decom- 
position goes  on  readily,  usually  have  a  large  quantity  of 
carbon  dioxide. 

185.  Production  of  carbon  dioxide  in  soils.  —  It  has 
already  been  shown  that  plant  roots  give  off  a  considerable 
quantity  of  carbon  dioxide  throughout  the  growth  of  the 


146  SOILS   AND   FERTILIZERS 

plant  (§  126).  This,  however,  does  not  account  for  the 
gas  that  is  formed  in  soils  on  which  no  plants  grow.  For 
this  the  germ  life  of  the  soil  is  responsible.  These  organisms 
consume  fresh  air  and  give  off  carbon  dioxide  in  the  process 
of  their  growth.  In  soils  that  contain  a  large  and  active  pop- 
ulation of  microorganisms  there  is  more  carbon  dioxide  formed 
than  in  a  more  nearly  sterile  soil. 

It  has  been  estimated  that  in  an  acre  of  ordinary  soil  to  a 
depth  of  four  feet  the  germs  produce  between  sixty-five  and 
seventy  pounds  of  carbon  dioxide  a  day  for  two  hundred 
days  in  the  year,  and  that,  during  the  growing  period,  the 
roots  of  oats  or  wheat  would  give  off  nearly  as  much  in  an 
acre. 

186.  Conditions  that  affect  the  quantity  of  carbon  dioxide 
in  soils.  —  As  carbon  dioxide  is  heavier  than  air,  the  quantity 
increases  with  depth.  In  warm  weather  more  carbon  dioxide 
is  formed  than  in  cold  because  the  germs  are  more  active. 
The  soil  moisture  exerts  an  influence  by  furnishing  the 
necessary  moisture  for  the  germs.  A  very  dry  or  a  very 
wet  soil  is  not  favorable  to  the  production  of  the  gas.  More 
carbon  dioxide  is  given  off  by  roots  during  the  blossoming 
period  than  at  other  stages  of  plant  growth,  consequently 
the  carbon  dioxide  content  of  soil  air  is  highest  about  the 
time  the  plants  are  in  blossom. 

187.  Usefulness  of  air  in  soils.  —  The  three  gases,  oxygen, 
nitrogen  and  carbon  dioxide,  that  go  to  make  up  practically 
all  of  the  soil  air  are  useful  in  bringing  about  those  processes 
that  make  soils  fertile.  Each  one  of  these  gases  has  its 
function  in  contributing  to  plant  growth  either  directly,  or 
by  taking  part  in  processes  that  render  the  soil  more  habitable 
to  plants.  The  functions  of  each  gas  will  be  discussed  sep- 
arately. 

188.  Oxygen.  —  This  constituent  of  soil  air  serves  the 
following  uses :    (1)  As  a  direct  food  material  for  plants, 


SOIL   AIR   AND   SOIL    TEMPERATURE  147 

and  as  a  means  of  promoting  in  the  plant  the  processes 
necessary  to  its  growth.  Roots  of  most  crops  must  have 
access  to  a  supply  of  oxygen. 

(2)  Decomposition  of  plant  residues  and  other  organic 
matter  in  soils  requires  the  presence  of  oxygen,  and  without 
decomposition  these  materials  would  accumulate  in  the  soil 
to  the  exclusion  of  higher  plant  life.  Decomposition  is 
also  of  use  in  the  production  of  carbon  dioxide,  the  function 
of  which  will  be  discussed  later,  and  in  the  formation  of 
compounds  of  organic  matter  with  mineral  matter,  decom- 
position serves  to  increase  the  availability  of  mineral  sub- 
stances (see  §  118). 

(3)  The  process  by  which  the  nitrogen  of  organic  matter  is 
converted  into  nitrates  can  proceed  only  in  the  presence  of 
oxygen. 

189.  Nitrogen.  —  Although  not  so  essential  as  oxygen, 
there  is  at  least  one  important  service  that  is  rendered  by 
the  nitrogen  of  soil  air.  This  is  to  furnish  the  nitrogen-fixing 
organisms  with  a  supply  on  which  they  may  draw  to  produce 
the  nitrogenous  compounds  that  become  incorporated  in 
leguminous  plants,  or  that  are  formed  directly  in  the  soil  by 
the  free-living  nitrogen  fixers. 

190.  Carbon  dioxide.  —  The  principal  service  that  carbon 
dioxide  renders  is  in  acting  as  a  solvent  for  the  mineral  matter 
of  the  soil.  For  this  purpose  it  is  itself  first  dissolved  in 
soil  water,  in  which  condition  it  is  a  weak  acid,  but  although 
weak,  its  universal  presence  and  constant  action  make 
it  an  effective  solvent.  It  dissolves  from  the  soil  more  or 
less  of  all  the  nutrient  substance's  required  by  plants  in  dis- 
tinctly greater  quantities  than  does  pure  water. 

A  number  of  experiments  in  which  carbon  dioxide  was 
artificially  brought  in  contact  with  soil  on  which  plants  were 
growing  have  resulted  in  producing  larger  crop  yields  than 
were  obtained  from  soil  not  so  treated.     It  cannot  be  con- 


148  SOILS  AND   FERTILIZERS 

eluded  from  this  that  an  artificial  supply  of  carbon  dioxide 
will  always  be  beneficial,  but  it  does  indicate  that  carbon 
dioxide  assists  in  making  the  plant  nutrients  more  available, 
although  in  many  soils  the  natural  supply  is  sufficient  for  its 
maximum  effect. 

191.  Control  of  the  volume  and  movement  of  soil  air.  — 
It  will  be  gathered  from  the  preceding  paragraphs  that  a 
good  supply  of  air  in  soil  with  opportunity  for  its  exchange 
with  atmospheric  air  is  desirable  for  a  number  of  reasons. 
These  conditions  can  be  controlled  by  man  to  some  extent. 
In  fact  those  operations  that  usually  promote  tilth  serve  at 
the  same  time  to  effect  a  desirable  condition  of  the  soil  with 
respect  to  air.  The  operations  by  which  man  may  control 
soil  air  are  as  follows  : 

1.  Tillage  of  all  kinds,  when  properly  done  and  at  the 
right  time,  increases  the  volume  of  air  in  most  soils  by  help- 
ing to  form  the  crumbly  structure,  and  by  disposing  of 
excess  water. 

2.  Both  farm  manure  and  lime  cause  an  increase  in  the 
carbon  dioxide  content  of  soil  air,  the  former  by  contribut- 
ing organic  matter  that  finally  decomposes,  the  latter  by 
hastening  decomposition  processes. 

3.  Underdrainage  by  removing  water  from  the  pore 
spaces  increases  the  volume  of  air  and  causes  its  movement. 

4.  Cropping  produces  channels  through  the  soil  where 
roots  have  decayed,  and  these  openings,  on  account  of  their 
large  number  and  ramifications  through  the  soil,  aid  greatly 
in  increasing  the  volume  of  soil  air. 

192.  Soil  temperature.  —  The  temperature  of  the  soil 
may  influence  plant  growth  both  directly  and  indirectly. 
The  direct  effect  is  to  be  found  in  the  plant  itself,  the  roots 
of  which  require  a  certain  degree  of  heat  before  they  begin 
to  function.  A  temperature  somewhat  above  the  freezing 
point  is  necessary  for  this  purpose,  some  common  plants 


SOIL  AIR  AND  SOIL    TEMPERATURE  149 

beginning  growth  slightly  above  that  point,  while  others 
need  several  degrees  higher  temperature.  This  is  also  true 
of  the  germination  of  seeds.  The  optimum  temperatures 
for  both  plants  and  seeds  are  considerably  higher.  A  tem- 
perature may  be  reached  at  which  both  plant  growth  and 
seed  germination  may  be  inhibited,  but  soils  rarely  reach 
such  a  degree  of  heat,  except  at  the  immediate  surface. 
The  problem  with  soils  usually  consists  in  bringing  them  to 
a  sufficiently  high  temperature  in  the  spring. 

The  indirect  influence  of  temperature  is  exerted  through 
the  germs  that  affect  plant  growth.  These,  like  higher 
plants,  require  a  certain  degree  of  warmth  before  growth 
begins  and  a  still  higher  temperature  before  they  reach  their 
full  activity.  It  often  occurs  that  crop  growth  is  well  under 
way  before  the  soil  is  sufficiently  warm  for  germs  to  function 
actively,  and  consequently  growth  is  checked  by  the  need 
of  nitrates,  which  have  not  been  formed  in  sufficient  quantity 
on  account  of  the  low  temperature.  This  condition  is  often 
demonstrated  by  the  yellow  color  of  the  leaves. 

193.  Sources  of  soil  heat.  —  The  greater  part  of  the  heat 
that  enters  the  soil  comes  directly  from  the  sun.  The  other 
possible  sources  are  the  organic  matter  in  the  soil  and  heat 
from  the  interior  of  the  earth.  Heat  produced  by  the  de- 
composition of  organic  matter  may  sometimes  be  a  factor 
wThen  the  proportion  is  large,  as  is  the  case  in  hotbeds  and 
gome  gardens,  but  ordinarily  it  may  be  left  out  of  considera- 
tion, as  may  also  the  heat  transmitted  from  the  center  of 
the  earth. 

194.  Relation  of  soil  temperature  to  atmospheric  tem- 
perature. —  Changes  in  temperature  of  the  atmosphere  are 
transmitted  to  the  soil,  although  the  extremes  are  never  so 
great  in  the  soil  as  in  the  atmosphere,  except  at  the  im- 
mediate surface,  and  the  extremes  become  less  as  the  depth 
increases.     In  summer  the  temperature  of  the  surface  soil  is 


150 


SOILS   AND   FERTILIZERS 


sometimes  higher  than  the  average  temperature  of  the  at- 
mosphere, or  even  than  the  maximum  air  temperature.  The 
soil  below  is  cooler  and  continues  to  decrease  in  temperature 
as  the  depth  increases.  For  that  reason  a  cellar  is  usually 
cooler  in  summer  than  is  the  outside  air.  On  the  other  hand, 
the  soil  does  not  become  as  cold  as  does  the  atmosphere  in 
winter,  and  below  a  few  feet,  in  temperate  regions,  the  soil 
does  not  freeze.  The  following  table  gives  the  mean  atmos- 
pheric temperatures,  and  the  soil  temperatures,  at  different 
depths  by  months  throughout  an  entire  year. 

Table  33.  —  Average  Monthly  Temperature  Readings  Taken 
at  Lincoln,  Nebraska 


January    . 
February 
March 
April    .     . 
May     .     . 
June     .     . 
July     .     . 
August      . 
September 
October    . 
November 
December 
Average 
Range 


Average  op  Twelve  Years 


Air 


25.2 
24.2 
35.8 
52.1 
61.9 
71.0 
76.0 
74.5 
67.6 
55.5 
38.7 
28.3 
50.9 
51.8 


3  Inches 
Deep 


27.8 
27.3 
37.2 
56.0 
67.5 
78.0 
83.6 
81.3 
73.4 
58.4 
40.9 
31.4 
55.3 
56.3 


12  Inches 
Deep 


31.2 
30.2 
35.4 
49.3 
60.7 
69.9 
75.7 
75.7 
69.2 
57.8 
44.7 
35.2 
52.9 
45.5 


36  Inches 
Deep 


38.5 
35.5 
35.8 
43.8 
53.3 
61.3 
67.4 
69.8 
67.6 
61.3 
52.2 
43.3 
52.5 
34.3 


195.  Factors  that  modify  soil  temperature.  —  There  are 
a  number  of  conditions  that  exert  an  influence  on  the  tem- 
perature of  the  soil,  important  among  which  are  (1)  the 
moisture  content,  (2)  the  color  of  the  soil,  (3)  the  slope  of 
the  land. 


SOIL   AIR   AND   SOIL    TEMPERATURE  lol 

A  wet  soil  is  always  a  cold  soil,  because  it  requires  about 
five  times  as  much  heat  to  raise  the  temperature  of  a  pound 
of  water  through  one  degree  of  temperature  as  it  does  to 
heat  a  pound  of  dry  soil  to  the  same  extent,  and  also  because 
when  the  water  becomes  warm  it  evaporates  and  in  so  doing 
removes  much  heat  from  the  soil.  The  evaporation  of  a 
pound  of  water  from  a  cubic  foot  of  soil  will  reduce  the  tem- 
perature of  the  soil  about  ten  degrees  Fahrenheit.  Provision 
for  having  the  water  drain  away  from  the  land  in  the  spring 
rather  than  evaporate  will  make  a  great  difference  in  the 
warmth  of  the  soil.  A  dark  soil  absorbs  more  heat  than  a 
light  colored  one.  This  is  enough  to  make  some  practical 
difference  in  a  region  having  a  short  growing  season. 

Land  that  slopes  to  the  south  absorbs  more  heat,  in  the 
North  Temperate  zone,  than  does  land  having  any  other 
slope,  and  the  nearer  the  slope  comes  to  making  a  right 
angle  with  the  sun's  rays  the  more  heat  it  will  absorb. 
An  east  or  west  slope  receives  more  heat  than  does  a  north 
slope.  For  this  reason  a  north  slope  is  especially  favorable 
for  grass  land,  because  grass  is  more  injured  by  midsummer 
heat  than  by  lack  of  sunshine. 

196.  Control  of  soil  temperature.  —  As  water  is  the 
substance  in  the  soil  most  difficult  to  heat,  it  is  evident  that 
good  drainage,  that  will  remove  the  excess  water  derived 
from  melted  snow  and  ice,  is  the  most  effective  means  of 
warming  land  in  the  spring,  in  order  that  it  shall  be  fitted 
for  planting.  If  water  can  pass  out  of  the  soil  by  under- 
drainage  it  then  becomes  desirable  to  curtail  evaporation, 
and  this  may  be  done  by  surface  tillage.  Evaporation  of 
water  removes,  as  we  have  seen,  large  quantities  of  heat. 
If  water  can  be  removed  in  any  other  way  much  heat  is 
saved.  In  regions  having  hot  spring  days  the  loss  by  evapo- 
ration may  be  so  large  that  more  water  is  removed  than  is 
desirable  and  yet  the  soil  may  lack  the  necessary  warmth. 


152  SOILS   AND   FERTILIZERS 

Sandy  soils  are  less  likely  to  be  cold  in  spring  than  are 
clay  soils,  because  the  former  usually  hold  water  less  tena- 
ciously. In  vineyards  a  covering  of  stones  on  the  soil 
has  been  found  to  facilitate  the  warming  of  the  soil  in  the 
spring,  but  it  is  doubtful  whether,  in  view  of  their  other  dis- 
advantages, stones  are  desirable. 

Good  tilth  is,  next  to  drainage,  the  best  aid  to  warming  soil 
in  spring,  as  it  allows  the  water  to  pass  down  into  the  lower 
soil  and  thus  decreases  evaporation  from  the  surface.  Har- 
rowing in  the  spring  produces  this  result,  while  rolling,  by 
compacting  the  surface,  increases  evaporation  and  cools  the 
soil. 

QUESTIONS 

1 .  Describe  the  conditions  that  govern  the  volume  of  air  in  soils . 

2.  State  the  two  principal  factors  that  affect  the  movement 
of  soil  air. 

3.  How  does  the  composition  of  soil  air  differ  from  that  of 
atmospheric  air  ? 

4.  What  are  the  sources  of  carbon  dioxide  in  soil  air  ? 

5.  What  are  the  functions  of  the  oxygen  of  soil  air  ? 

6.  What  are  the  functions  of  the  nitrogen  of  soil  air  ? 

7.  What  are  the  functions  of  the  carbon  dioxide  of  soil  air? 

8.  In  what  ways  may  the  volume  and  movement  of  soil  air 
be  controlled  ? 

9.  Describe  the  direct  and  the  indirect  effect  of  temperature 
on  plant  growth. 

10.  What  are  the  sources  of  soil  heat  ? 

11.  Describe  three  factors  that  modify  soil  temperature. 

12.  By  what  means  may  soil  temperature  be  controlled  ? 

LABORATORY  EXERCISE 

Exercise  I.  —  Movement  of  soil  air  as  influenced  by  texture  and 
moisture. 

Materials.  —  Dry  sand,  dry  clay  loam,  6"  funnels,  cotton,  aspi- 
rating bottles  (10  liter). 

Procedure.  —  Place  a  large  funnel  through  the  cork  of  an  aspi- 
rating bottle,  fill  to  the  mark  with  water,  as  shown  in  Fig.  26. 
Place  a  small  piece  of  cotton  in  the  bottom  of  the  funnel  and  fill  with 


SOIL   AIR   AND   SOIL    TEMPERATURE 


153 


a  definite  volume  of  sand.  Now  start  as- 
piration by  opening  the  water-cock  of  the 
bottle.  When  aspiration  has  become  con- 
stant, note  time  necessary  to  draw  one  liter 
of  air  through  the  sand. 

Using  clay  loam  in  place  of  sand,  run 
the  experiment  again,  bringing  the  water  in 
the  aspirating  bottle  up  to  its  original  mark 
before  starting.  The  time  necessary  to  pull 
a  liter  of  air  through  each  soil  serves  as  a 
measure  of  the  comparative  rate  of  possible 
air  movement  through  them. 

Without  removing  the  clay  loam  from  the 
funnel,  add  enough  water  to  bring  it  to 
optimum  moisture  condition.  Repeat  the 
test  above.     Explain  results.  Fig.    26.  —  Apparatus 

Exercise  II.  —  The  presence  of  carbon  *£/*$ y Jg  ^tment 
dioxide  m  soil  an*.  through  soils.     (A)  soil  in 

Materials.  —  Box  of  rich  soil  in  good  mois-  funnel,  (B)   cotton  sup- 
ture  condition,  flask,  limewater,  tubes.  P1°rt;7)f)  ater™^  ^ 

Procedure.  —  Equip  a  flask  or  bottle  as 
shown  in  Fig.  27  so  that  air  from  the  soil  may  be  sucked  into  the 
limewater.    The  turbidity  of  the  limewater  indicates  the  presence 
of  carbon  dioxide. 


j^="=J\ 


5ucuon 


Tube  for  ujtlhdrauJinq 
/   soil  air 


Coarse  sand 


Fig.  27.  —  Apparatus  prepared  for  the  demonstration  of  the  presence  of 
carbon  dioxide  in  soil  air. 


154 


SOILS   AND   FERTILIZERS 


First  pull  atmospheric  air  into  the  limewater  for  five  minutes. 
Note  results.  Now  connect  flask  to  tube  extending  into  the  soil  and 
draw  in  soil  air.  What  conclusions  do  you  come  to  regarding  the 
relative  carbon  dioxide  content  of  soil  air  and  atmospheric  air  ? 
What  is  the  function  of  carbon  dioxide  in  the  soil  ? 

Exercise  III.  —  Production  of  carbon  dioxide  by  bacteria. 

Materials.  —  Flask,  limewater  and  moist 
rich  soil. 

Procedure.  —  Place  a  small  amount  of 
limewater  in  a  flask  and  then  suspend  in 
the  flask  over  the  limewater  a  bag  of  rich, 
moist  soil.  Stopper  tightly  and  allow  to 
stand  for  a  week.  Note  the  turbidity  of  the 
limewater.     Explain  the  results. 

Exercise  IV.  —  Temperature  and  color. 
Materials.  —  Coal  dust  and  calcium  hy- 
drate.    Thermometers. 

Procedure.  —  Divide  a  small  plat  of 
smooth,  level  soil  into  three  portions. 
Leave  one  part  untouched,  cover  one  with  a 
thin  coating  of  coal  dust  and  the  other  with 
a  coating  of  calcium  hydrate.  On  a  warm, 
sunny  afternoon  take  the  temperatures  of 
each  at  one,  three  and  six  inches  deep. 
Tabulate  and  give  a  practical  explanation 
of  the  data  obtained. 
Exercise  V.  —  Slope  and  temperature. 
Materials.  —  Thermometers. 

Procedure.  —  On  a  warm,  sunny  day  take  temperature  at  one, 
three  and  six  inch  depths  on  a  south  slope,  north  slope  and  level 
land,  being  careful  to  select  for  the  observations  soils  having  the 
same  texture  and  moisture  contents.  Tabulate  data  and  explain 
the  practical  relationships  between  temperature  and  slope  of  land. 
Exercise  VI.  —  Drainage  and  temperature. 
Materials.  —  Soil,  two  jars,  thermometer. 

Procedure.  —  Prepare  two  large  jars  of  moist  soil.  Stir  one  until 
two  or  three  inches  of  the  top  soil  is  dry.  Add  water  to  the  other 
until  it  is  saturated.  Set  these  jars  of  soil  in  the  sunshine  out  of 
doors  on  a  warm  day.  After  two  hours  take  the  temperature  of 
the  two  soils  at  one  inch  and  three  inches  in  depth.     Tabulate  data. 


Fig.  28.  —  Production 
of  carbon  dioxide  by 
germs  in  soil.  (^4.)  tight 
stopper,  (B)  flask  con- 
taining limewater,  (C) 
small  bag  containing 
moist  soil  suspended  from 
stopper,  (D)  limewater. 


CHAPTER  XI 

NITROGENOUS  FERTILIZERS    • 

We  have  seen  that  nitrogen  exists  in  soils  in  several  differ- 
ent forms,  as  organic  matter,  ammonia  and  nitrates,  and  that 
it  msiy  be  transformed  from  one  to  another  of  these,  depend- 
ing on  the  conditions  that  obtain  in  the  soil  itself.  Ferti- 
lizers used  for  their  nitrogen  may  have  this  nitrogen  present 
in  any  one  or  more  of  these  forms,  and  when  incorporated 
with  the  soil,  transformation  will  proceed  according  to  the 
same  laws  that  govern  the  soil  nitrogen.  This  is  important 
because  nitrogen  is  more  readily  used  by  crops  in  some 
forms  than  in  others. 

197.  Relative  quantities  of  the  different  forms  of  nitrogen 
in  soils.  —  One  would  naturally  expect  to  find  the  greater 
part  of  the  supply  of  soil  nitrogen  in  the  most  stable  forms, 
and  this  is,  in  fact,  the  case.  The  uncombined  nitrogen  of  the 
air  constitutes  the  largest  supply  because  of  its  diffusibility 
with  the  atmospheric  air.  Next  in  quantity  is  the  nitrogen 
of  organic  compounds,  ranging  from  0.05  to  0.3  percent  or 
1000  pounds  to  6000  pounds  to  the  acre  in  the  furrow  slice 
of  ordinary  arable  land  and  slightly,  but  appreciably,  soluble 
in  water.  In  upland  cultivated  soils  the  nitrogen  of  nitrate 
salts  forms  the  next  largest  supply,  but  rarely  exceeds  20 
percent  of  the  total  combined  nitrogen  of  the  soil. 

In  inundated  soils,  the  nitrogen  of  ammonia  salts  and 
nitrites  forms  a  larger  proportion  of  the  soil  nitrogen  than 
does  the  nitrate  nitrogen,  but  in  well-aerated  soils  these  com- 
pounds exist  in  very  small  quantities. 

155 


156  SOILS   AND   FERTILIZERS 

198.  Forms  in  which  nitrogen  is  absorbed  by  plants.  — 
The  utilization  of  atmospheric  nitrogen  by  leguminous  plants 
and  by  a  few  others  that  have  nodule-bearing  roots  has  been 
established  beyond  question ;  but  the  extent  to  which  this 
form  of  nitrogen  may  be  utilized  by  other  plants,  or  the  kinds 
of  plants  that  have  the  ability  to  use  it,  are  subjects  on  which 
opinions  differ.  It  is  sufficient  to  say  that  such  plants  as 
red  clover,  alfalfa,  peas,  beans,  vetch,  and  so  on,  are  able  to 
use  atmospheric  nitrogen.  It  must  be  remembered,  however, 
that  they  also  use  nitrogen  that  is  in  the  soil  itself  and  that 
they  may  remove  large  quantities  of  this  material. 

199.  Nitrates  as  plant-food  material.  —  Most  upland 
plants  used  in  agriculture  appear  to  absorb  most  of  their 
nitrogen  in  the  form  of  nitrates.  This  it  will  be  remem- 
bered is  the  final  form  in  which  nitrogen  appears  when  ni- 
trogenous substances  undergo  normal  decomposition  in  soil. 
The  nitrogen  of  the  various  nitrogen  carrying  fertilizers  is 
finally  converted  into  nitrate  in  the  soil. 

200.  Absorption  of  ammonia  by  agricultural  plants. — 
Ammonia  is  rarely  found  in  soils,  except  when  they  are 
saturated  with  water.  Plants  like  rice,  that  grow  on  water- 
covered  soil,  can  utilize  ammonia ;  in  fact,  rice  has  been  found 
to  make  a  better  growth  on  ammonium  compounds  than  on 
nitrates.  This  is  a  case  in  which  the  plant  has  evidently 
adapted  itself  to  its  surroundings,  for  upland  rice  presumably 
uses  nitrate  nitrogen.  However,  some  dry  land  plants  can 
also  use  ammonia.  It  has  been  found,  for  instance,  that 
peas  obtained  nitrogen  as  readily  .from  ammonium  salts  as 
from  sodium  nitrate.  On  the  other  hand  wheat  plants,  while 
able  to  secure  some  nitrogen  from  ammonia,  have  been  found 
to  grow  much  better  when  they  could  obtain  nitrates. 

201.  Direct  utilization  of  organic  nitrogen  by  crops.  — 
One  of  the  early  beliefs  in  regard  to  plant  nutrition  was 
that  organic  matter  was  directly  absorbed  by  plants  and  that 


•; 

m 

-JIB 

/4»'»« 

[Mi 

f     n 

i  • '  ^i 

/« 

: 

'^i 

ffl'a- 

iwf 

jlJKu'1, 

r  m 

IWkaR     df3r^k'x 

A 

: 

ft'  kAH     !i 

IB  ■ 

I  7     frvf/jl      / 

Hv' 

7      ^ 
|  i 

Wmjki  j 

Plate  XII.  Fertilizer  Tests.  —  Some  soils  respond  best  to  one 
fertilizer  constituent,  others  to  another.  Note  that  the  best  growth  of 
oats  in  the  upper  figure  is  in  the  vessels  that  received  nitrogen.  In  the 
lower  figure  the  best  growth  is  in  the  vessel  that  received  phosphoric  acid. 


NITROGENOUS   FERTILIZERS  157 

it  furnished  their  chief  supply  of  food.  Opinion  afterwards 
swung  to  the  opposite  extreme,  and  it  was  generally  held 
that  no  organic  matter  is  absorbed  by  agricultural  plants. 
Lately,  however,  it  has  been  shown  that  many  crops  can  use 
nitrogenous  organic  matter,  and  an  organic  compound  called 
creatinin,  that  has  been  isolated  from  soil,  was  found  to 
produce  a  better  growth  of  wheat  seedlings  than  did  sodium 
nitrate.  This  may  account  in  part  for  the  high  fertilizing 
value  of  farm  manure.  Many  crops,  especially  among 
garden  vegetables,  are  most  successfully  grown  only  when 
supplied  with  organic  nitrogenous  materials. 

202.  Forms  of  nitrogen  in  fertilizers.  —  There  are  many 
different  kinds  of  material  used  to  provide  nitrogen  in  com- 
mercial fertilizers.  Their  value  varies  considerably,  because 
the  nitrogen  in  some  is  not  so  readily  available  as  it  is  in  others. 
In  some  the  nitrogen  is  in  the  form  of  nitrate,  in  others  am- 
monia, but  most  of  the  mixed  fertilizers  contain  some  or  all 
of  their  nitrogen  in  the  form  of  organic  matter. 

203.  Nitrate  of  soda.  —  This  material  is  found  in  natural 
deposits  in  northern  Chili,  where  it  is  mined  in  enormous 
quantities  and  shipped  to  most  of  the  European  countries 
and  to  the  United  States.  It  is  refined  before  shipment, 
reaching  this  country  nearly  96  percent  pure.  Between  15 
and  16  percent  of  the  total  material  is  nitrogen.  The  im- 
purities are  not  of  a  kind  to  be  injurious  to  plants. 

This  fertilizer  is  easily  soluble  in  water  and  is  readily  ab- 
sorbed by  most  farm  crops.  It  is  the  most  active  form  of 
nitrogen.  Because  it  does  not  need  to  be  acted  on  by  soil 
organisms  before  being  used  by  plants,  it  is  of  great  value  in 
starting  growjth-in  the  early  spring,  before  the  soil  is  warm 
enough*  to  cause  a  conversion  of  the  nitrogen  of  soil  organic 
matter,  or  of  farm  manure  into  nitrates.  It  will  be  remem- 
bered that  nitrates  are  largely  washed  out  of  the  soil  during 
the  fall  and  winter  and  that  there  is  not  usually  enough 


158 


SOILS   AND   FERTILIZERS 


of  this  form  of  nitrogen  to  start  plant  growth  early  in  the 
spring. 

204.  Crops  markedly  benefited  by  nitrates.  —  Winter 
grain  is  usually  benefited  by  an  application  of  25  to  50 
pounds  to  the  acre  of  nitrate  of  soda  about  the  time  that 
growth  begins  in  the  spring.  The  phosphoric  acid  and  potash 
fertilizers  may  be  applied  in  the  fall. 

Timothy  meadow  responds  wonderfully  to  a  top  dressing 
of  nitrate  when  the  plants  first  show  signs  of  life.  Not  only 
is  the  yield  of  hay  increased,  but  the  sod  is  thickened,  which 
increases  its  value  as  a  manure  for  succeeding  crops.  Phos- 
phoric acid  and  potash  fertilizers  should  be  applied  at  the 
same  time.  The  following  table  shows  the  increased  yield 
of  hay  and  succeeding  grain  crops  obtained  from  applications 
of  nitrate  fertilizer  applied  only  to  the  grass  crops.  Note 
the  increased  yield  of  hay  and  grain  from  larger  applications 
of  nitrate  when  the  other  fertilizers  are  not  increased,  and 
also  the  striking  effect  of  the  better  sod  on  the  yield  of  corn, 
which  crop  was  not  fertilized.  This  offers  a  rational  method 
for  producing  organic  manure  from  mineral  fertilizers. 

Table  34.  —  Yields  op  Hay  and  Grain  on  Unfertilized  Soil 
and  on  Soil  Fertilized  for  Hay  but  not  for  Grain 


Plat 

No. 

Pounds  Fertilizer  per  Acre 

Yields  of  Crops  per  Acre 

Hay  3 

Years 

Corn 

Oats 

Wheat 

720 
721 

725 
726 

No  fertilizer        

f  160  lbs.  nitrate  of  soda 

<  80  lbs.  muriate  of  potash  >    .     . 
1  320  lbs.  acid  phosphate      j 

|  320  lbs.  nitrate  of  soda 

<  80  lbs.  muriate  of  potash  }    .     . 
[  320  lbs.  acid  phosphate      J 

No  fertilizer        

Tons 
4.5 

8.4 

10.5 
4.2 

Bu. 
35.1 

55.7 

62.9 
33.4 

Bu. 

33.5 
36.4 

38.2 
29.7 

Bu. 

19.3 

18.7 

19.5 
22.8 

NITROGENOUS   FERTILIZERS  159 

By  the  time  the  wheat  crop  was  raised  the  beneficial  effect 
of  the  timothy  sod  had  disappeared. 

Many  kinds  of  garden  vegetables  must  have  a  rapid 
growth  in  order  to  have  the  succulence  upon  which  their 
value  largely  depends.  To  secure  this  quick  growth  nitrate 
of  soda  gives  an  excellent  form  of  nitrogen  on  account  of  its 
readjr  availability.  As  previously  noted,  however,  it  is  not 
an  adequate  substitute  for  organic  nitrogen  for  all  kinds  of 
garden  crops. 

205.  Effect  of  nitrate  of  soda  on  soils.  —  Nitrates  are 
easily  leached  from  soils,  and  for  that  reason  nitrate  of  soda 
should  not  be  applied  in  the  autumn  as  it  will  be  lost,  in  large 
part,  during  the  fall  and  winter.  Even  when  applied  pre- 
paratory to  planting,  it  should  not  be  used  in  excessive  quan- 
tities at  one  time,  but  if  large  applications  are  necessary 
apply  part  after  the  plants  have  made  some  growth. 

It  has  been  found  that  the  continued  and  abundant  use  of 
nitrate  of  soda  causes  some  soils  to  become  deflocculated, 
resulting  in  a  puddled  condition  when  the  soil  is  worked  wet 
and  a  cloddy  condition  when  dry.  This,  however,  is  not 
likely  to  occur  with  any  ordinary  use  of  the  fertilizer.  On 
acid  soils  it  serves  a  double  purpose,  for  it  tends  to  correct 
acidity. 

206.  Sulfate  of  ammonia.  —  The  source  of  supply  of  this 
fertilizer  is  coal,  which  when  distilled,  as  is  done  in  the  man- 
ufacture of  illuminating  gas,  or  in  the  production  of  coke, 
yields  among  other  products  ammonia  from  which  sulfate 
of  ammonia  is  made.  The  industry  has  grown  enormously 
in  recent  years,  but  has  by  no  means  reached  its  maximum, 
as  of  the  hundreds  of  thousands  of  tons  of  coal  burned  an- 
nually for  the  manufacture  of  coke  in  this  country  barely 
more  than  one-half  is  used  for  the  production  of  ammonia. 
There  are  still  great  possibilities  for  obtaining  nitrogen  from 
this  source. 


160  SOILS   AND   FERTILIZERS 

207.  Composition  of  sulfate  of  ammonia.  —  There  is  more 
nitrogen  in  a  ton  of  this  fertilizer  than  in  any  other.  The 
commercial  material  usually  contains  about  20  percent  of 
nitrogen,  which  is  from  eighty  to  one  hundred  pounds  more 
than  is  contained  in  a  ton  of  nitrate  of  soda.  It  is  easily 
soluble  in  water,  but  when  applied  to  soils  the  ammonia  is 
absorbed,  and  probably  very  little  of  it  is  taken  up  directly 
by  plants.  On  the  other  hand,  the  absorbed  ammonia 
nitrifies  readily,  especially  if  there  is  plenty  of  lime  in  the 
soil,  and  the  nitrates  thus  formed  may  readily  be  used  by 
plants. 

208.  Action  when  applied  to  soils.  —  A  pound  of  nitrogen 
in  the  form  of  sulfate  of  ammonia  has  slightly  less  value  than 
the  same  quantity  in  the  form  of  nitrate.  If  the  soil  to  which 
it  is  applied  is  in  need  of  lime,  the  value  of  the  fertilizer  will 
be  less  than  if  sufficient  lime  be  present.  It  also  tends  to 
make  a  soil  acid  when  used  in  large  quantities  for  a  long 
period.  These  two  facts  make  it  apparent  that  lime  should 
be  abundantly  supplied  to  soils  on  which  this  fertilizer  is 
used.  Lime,  whether  it  is  applied  to  the  soil  or  is  naturally 
present,  serves  to  neutralize/  the  acid  formed  when  the  am- 
monia is  converted  into  niwic  acid  by  soil  bacteria,  which  is 
the  process  by  which  nitrates  are  formed,  and  also  to  neutral- 
ize the  sulfuric  acid  left  in  the  soil  when  the  ammonia  is 
changed  by  this  process. 

The  nitrates  resulting  from  the  fermentation  of  sulfate  of 
ammonia  are  quickly  leached  out  of  the  soil  when  no  plants 
are  growing  on  it ;  therefore  sulfate  of  ammonia  should  not 
be  applied  at  that  time.  In  England  the  following  losses 
of  nitrogen  occurred  from  plats  on  which  nitrate  and  am- 
monium salts  were  used,  and  on  which  crops  were  grown. 
The  term  "  minerals  "  is  here  used  to  mean  phosphoric  acid 
and  potash  fertilizers. 


NITROGENOUS   FERTILIZERS 


161 


Table  35.  —  Pounds  of  Nitrogen  in  Drainage   Water  from 
Soil  Treated  with  Nitrate  and  Ammonia  Fertilizers 


1879-1880 

1880 

-1881 

Treatment 

Spring 

Harvest 

Spring 

Harvest 

Sowing 

to 

Sowing 

to 

to 

Spring 

to 

Spring 

Harvest 

Sowing 

Harvest 

Sowing 

Unmanured 

1.7 

10.8 

0.6 

17.1 

Mineral  fertilizers  only      .... 

1.6 

13.3 

0.7 

17.7 

Minerals  +  400  pounds  ammonium 

salts 

18.3 

12.6 

4.3 

21.4 

Minerals  +  550   pounds   nitrate   of 

soda 

45.0 

15.6 

15.0 

41.0 

Minerals  +  400  pounds  ammonium 

salts  applied  in  autumn      .     .     . 

9.6 

59.9 

3.4 

74.9 

400  pounds  ammonium  salts  alone  . 

42.9 

14.3 

7.4 

35.2 

400  pounds  ammonium  salts  +  sul- 

phate of  potash 

19.0 

16.4 

3.7 

25.3 

Estimated  drainage  in  inches      .     . 

11.1 

4.7 

1.8 

18.8 

These  figures  show  a  very  considerable  loss  of  nitrogen 
from  the  nitrogen-fertilized  plats,  with  a  somewhat  greater 
loss  from  the  nitrate-treated  plats  than  from  those  receiv- 
ing ammonia.  Neither  of  these  fertilizers  is  well  designed 
to  add  to  the  total  supply  of  nitrogen  in  the  soil,  for  which 
purpose  a  less  easily  nitrifiable  fertilizer  must  be  used. 

209.  Cyanamid.  —  Within  recent  years  it  has  been  found 
possible  to  take  nitrogen  from  the  atmosphere  and  combine 
it  with  lime  for  use  as  a  fertilizer.  Two  different  materials 
are  manufactured.  One  is  called  cyanamid,  the  other 
nitrate  of  lime.  Both  are  produced  by  the  use  of  powerful 
currents  of  electricity,  but  the  processes  are  essentially  dif- 
ferent and  only  the  cyanamid  is  now  being  manufactured  in 
the  United  States,  and  it  alone  will  be  discussed  in  this  book. 

210.  Composition  of  cyanamid.  —  The  word  cyanamid  is 


162  SOILS   AND   FERTILIZERS 

merely  a  trade  name.  Another  name  that  has  been  used  is 
lime  nitrogen.  The  latter  is  good  because  it  emphasizes  the 
fact  that  the  fertilizer  contains  lime,  which  is  a  point  in  its 
favor,  as  the  lime  helps  to  overcome  soil  acidity.  There  is 
about  26  percent  of  caustic  lime  in  the  fertilizer.  How- 
ever, in  the  quantities  in  which  fertilizers  are  used  the 
sweetening  effect  of  the  lime  would  not  go  very  far.  The 
fertilizer  usually  contains  between  15  and  16  percent  of  nitro- 
gen, which  puts  it  on  a  par  with  nitrate  of  soda  in  this 
respect. 

211.  Changes  in  the  soil.  —  Cyanamid  must  be  decom- 
posed in  the  soil  before  its  nitrogen  becomes  available  to 
plants.  It  is,  therefore,  not  as  rapid  in  its  effects  as  is  nitrate 
of  soda,  but  resembles  sulfate  of  ammonia  in  this  respect. 

Under  some  conditions  products  may  be  formed  during  its 
decomposition  that  are  more  or  less  injurious  to  plants. 
This  is  said  to  be  true  when  the  fertilizer  is  incorporated 
with  water  saturated  soil  or  very  acid  soil.  As  decomposi- 
tion proceeds  these  injurious  substances  are  destroyed.  In 
order  to  be  sure  that  no  injury  will  be  done  to  plants,  cyan- 
amid should  be  applied  at  least  a  week  before  planting. 

It  is  not  well  adapted  to  use  on  very  sandy  soils,  nor  does 
it  give  its  best  results  when  used  as  a  top  dressing,  as  it  re- 
quires incorporation  with  the. soil  for  its  proper  decomposi- 
tion. Ordinarily  its  fertilizing  value  is  not  greatly  below  that 
of  sodium  nitrate,  and  is  about  equal  to  that  of  sulfate  of 
ammonia. 

212.  Fertilizers  containing  organic  nitrogen.  —  There  are 
a  great  many  materials  containing  organic  nitrogen  that 
are  used  as  fertilizers.  As  many  of  them  are  of  little  or  no 
value  for  other  purposes  they  would  be  wasted  if  not  used  to 
benefit  the  land.  There  is  very  great  diversity  as  to  their 
fertilizer  value,  but  in  general  the  availability  of  the  nitrogen 
to* plants  is  less  than  that  of  nitrate  of  soda.     In  order  that 


NITROGENOUS  FERTILIZERS  163 

their  nitrogen  shall  become  available,  the  substances  them- 
selves must  decompose  in  the  soil,  the  nitrogen  undergoing 
the  usual  transformations. 

Many  of  the  organic  fertilizers  contain  phosphoric  acid, 
or  potash,  or  both.  These  ingredients  add  to  the  value  of 
the  fertilizer.  They  will  be  discussed  under  the  heads  of 
(1)  vegetable  products,  (2)  animal  products,  (3)  guano. 

213.  Vegetable  products.  —  Among  these  are  cottonseed 
meal,  linseed  meal  and  castor  pomace  together  with  other 
materials  that  are  less  used  and  that  will  not  be  discussed 
here. 

The  meals  here  mentioned  are  primarily  stock-foods  and 
are  more  profitably  fed  to  live-stock,  the  resulting  manure 
being  applied  to  the  soil,  than  used  directly  as  fertilizer. 
Nevertheless,  cottonseed  meal  is  used  extensively  as  a  fer- 
tilizer and  linseed  meal  to  a  less  extent.  The  former  is  much 
used  for  tobacco  of  better  grades  and  as  a  top  dressing  for 
lawn  grasses,  as  it  does  not  have  the  offensive  odor  that  char- 
acterizes many  of  the  organic  fertilizers. 

Cottonseed  meal  contains  between  6  and  7  percent  of  nitro- 
gen when  free  from  hulls,  and  4  percent  when  these  are  pres- 
ent. It  also  contains  about  2.5  percent  of  phosphoric  acid 
and  1.5  percent  of  potash. 

Linseed  meal  contains  about  5.5  percent  of  nitrogen,  and 
between  1  and  2  percent  of  phosphoric  acid  and  of  potash. 

Castor  pomaj2%  which  is  the  residue  after  the  extraction 
of  castor  oirlrom  the  beans,  has  a  nitrogen  content  of  between 
5.5  and  6  percent,  and  a  rather  variable  amount  of  phos- 
phoric acid  and  potash. 

214.  Animal  products.  —  These  include  the  slaughter  house 
products  among  which  are  red  dried  blood,  with  about  13 
percent  of  nitrogen ;  black  dried  blood,  with  6  to  i2  percent 
nitrogen ;  dried  meat  and  hoof -meal,  with  12  to  13  percent 
nitrogen;    tankage,  of  which  the  concentrated  product  has 


164  SOILS  AND  FERTILIZERS 

a  nitrogen  content  of  from  10  to  12  percent,  and  crushed 
tankage,  that  has  from  4  to  9  percent  nitrogen.  Leather 
meal  and  wool  and  hair  waste  may  also  be  mentioned  but 
they  have  only  a  small  fertilizer  value.  Ground  fish  or  fish 
waste  is  also  sold  as  a  fertilizer  and  usually  contains  about 
8  percent  of  nitrogen. 

Dried  blood  is  the  most  readily  decomposed  of  these 
products,  and  its  nitrogen  is  in  the  most  available  form. 
It  also  contains  a  small  quantity  of  phosphoric  acid.  It  is 
slower  in  its  action  than  either  nitrate  of  soda  or  sulfate  of 
ammonia.  With  this,  as  with  all  the  animal  products,  the 
soil  should  be  in  a  condition  favorable  to  decomposition  of 
organic  matter  and  to  the  formation  of  nitrates. 

Dried  meat  contains  a  high  percentage  of  nitrogen,  but 
does  not  decompose  so  easily  as  does  dried  blood,  and  is  not  so 
desirable  a  form  of  nitrogen.  It  may  be  fed  to  hogs  or  poultry 
to  advantage,  and  the  resulting  manure  is  very  high  in  nitro- 
gen. 

Hoof-and-horn  meal  is  high  in  nitrogen,  but  decomposes 
slowly.  Its  nitrogen  is  less  active  than  dried  blood  or  meat. 
It  is  useful  to  increase  the  store  of  nitrogen  in  a  depleted  soil. 

Tankage  is  highly  variable  in  composition.  The  concen- 
trated tankage,  being  more  finely  ground,  undergoes  more 
readily  the  decomposition  necessary  for  the  utilization  of  its 
nitrogen. 

Leather  meal  and  wool  and  hair  waste  when  untreated 
are  in  such  a  tough  and  undecomposable  condition  that  they 
may  remain  in  the  soil  for  years  without  losing  their  structure. 
They  are  not  to  be  recommended  as  manures. 

215.  Fish  waste.  —  The  material  sold  under  this  name  is 
usually  waste  from  canning  factories,  and  consists  of  the 
heads,  tails,  bones,  entrails  and  all  other  discarded  portions 
of  the  fish  that  are  canned.  As  a  fertilizer  it  acts  very  slowly 
and  is  not  at  all  adapted  to  crops  that  make  their  growth  in 


NITROGENOUS  FERTILIZERS      .  165 

the  early  spring.     It  is  better  adapted  to  sandy  soils  than  to 
heavy  ones. 

216.  Guano.  —  This  was  formerly  a  very  important  fer- 
tilizing material,  but  there  is  comparatively  little  of  it  im- 
ported into  this  country  at  present,  because  the  world's 
supply  is  nearly  exhausted.  It  consists  of  the  excrement  and 
carcasses  of  sea  fowl.  The  composition  of  guano  depends 
on  the  climate  of  the  region  in  which  it  is  found.  Guano  from 
an  arid  region  contains  much  more  nitrogen  and  potash  than 
that  from  a  region  of  more  rainfall,  because  these  constituents 
have  been  leached  out  of  the  latter.  All  of  the  plant-food 
materials  contained  in  guano  are  in  a  readily  available  con- 
dition, and  its  fertilizing  value  is  high. 

217.  Effects  of  nitrogen  on  plant  growth.  —  The  all  impor- 
tant part  that  nitrogen  plays  in  plant  growth  is  that  of  an 
indispensable  constituent  of  protein,  which  is  the  basic  sub- 
stance in  every  cell  of  every  plant.  It  is  therefore  concerned 
in  the  formation  of  every  part  of  the  plant.  If  the  supply 
of  nitrogen  is  inadequate,  the  effect  is  to  decrease  the  yield 
of  the  crop,  especially  the  leaves,  stems,  stalks  or  straw, 
while  the  quantity  of  grain  produced  is  not  curtailed  to  the 
same  extent.  On  the  other  hand,  an  excess  of  available  nitro- 
gen causes  an  abundant  growth  of  the  vegetative  parts  of  the 
plant  rather  than  of  the  seed  or  grain.  As  a  result,  in 
cereals  the  straw  becomes  so  long  and  weak  that  the  plants 
fall  down  or  "  lodge."  Grass  crops  are  less  likely  to  suffer 
from  an  excess  of  nitrogen  than  are  cereals,  and  nitrogen 
is  particularly  beneficial  to  the  grasses.  Many  vegetables 
that  are  grown  for  their  vegetative  parts  can  utilize  to  good 
advantage  a  large  quantity  of  nitrogen.  If  nitrogen  is  not 
present  in  sufficient  quantity  for  cereals,  the  kernels  are 
shriveled  and  light.  There  can  be  no  doubt  that  the  lack  of  a 
readily  available  supply  of  nitrogen  at  critical  periods  in  the 
growth  of  plants  is  a  frequent  cause  of  curtailed  crop  yields. 


166  SOILS  AND   FERTILIZERS 

Another  effect  of  excess  nitrogen  supply  is  to  delay  the 
ripening  of  crops.  This  is  often  seen  in  orchards  that  receive 
clean  cultivation  throughout  the  summer.  The  large  supply 
of  nitrogen  thus  made  available,  as  well  as  the  moisture  re- 
tained in  the  soil,  serves  to  retard  ripening  and  the  immature 
wood  is  likely  to  be  injured  by  winter  temperatures.  In 
regions  having  short,  but  usually  hot  seasons,  cereals  are 
sometimes  delayed  in  ripening  until  injured  by  frost. 

Sometimes  the  quality- of  crops  may  be  injured  by  an  ex- 
cess of  nitrogen.  Barley  deteriorates  in  its  malting  qualities, 
and  peaches  in  flavor  when  too  much  nitrogen  is  supplied. 

The  percentage  of  nitrogen  may  be  increased  in  some  crops 
by  supplying  a  large  quantity  of  available  nitrogen.  Tim- 
othy hay  responds  in  this  way,  as  do  many  vegetables,  and  the 
straw  and  even  the  grain  of  cereals. 

Resistance  to  disease  is  often  decreased  when  nitrogen  is 
abundant.  This  is  familiarly  exhibited  in  the  ease  with  which 
a  crop  of  wheat  or  oats  on  very  rich  soil  will  succumb  to  rust. 
There  are  numerous  cases  of  this  kind,  probably  due  to  a 
change  in  the  physiological  resistance  of  the  plant  to  the 
diseases  to  which  it  is  exposed. 

218.  Availability  of  nitrogenous  fertilizers.  —  It  has  been 
pointed  out  that  nitrates  are  the  form  in  which  nitrogen  is 
most  acceptable  to  the  larger  number  of  agricultural  plants, 
and  this  being  the  case  fertilizers  having  nitrates  offer  a  very 
readily  available  form  of  nitrogen.  Ammonium  salts  not 
being  so  readily  appropriated  by  most  plants  require  at 
least  partial  conversion  into  nitrates.  Ammonia  is  ab- 
sorbed by  soil,  but  in  its  absorbed  condition  readily 
undergoes  nitrification.  However,  there  is  apparently  some 
loss  or  conversion  into  an  insoluble  condition,  for  experiments 
have  generally  shown  that  there  is  rarely  quite  as  much  nitro- 
gen recovered  by  crops  from  sulfate  of  ammonia  as  from  ni- 
trate of  soda.     The  organic  nitrogenous  fertilizers  must  un- 


NITROGENOUS   FERTILIZERS 


167 


dergo  ammonification  and  nitrification  in  the  soil.     Some 
of  them  decompose  much  more  readily  than  others. 

In  order  to  ascertain  the  relative  degree  of  availability  of 
the  nitrogenous  fertilizers,  experiments  have  been  conducted 
by  numerous  investigators  in  which  they  have  used  one  of 
these  fertilizers  on  one  or  more  plats  of  land,  or  in  one  or  more 
vessels  of  soil,  and  other  nitrogenous  fertilizers  in  a  similar 
way.  It  is,  of  course,  always  necessary  that  there  shall  be 
an  abundance  of  all  the  other  plant-food  materials.  These 
experiments  were  repeated  for  several  years  with  different 
crops,  at  the  end  of  which  time  a  comparison  was  made  of  the 
yields  of  the  crops  on  the  soil  treated  with  the  different  fer- 
tilizers. In  Table  36  the  results  of  some  of  these  experiments 
are  stated,  with  the  yields  obtained  with  nitrate  of  soda 
taken  as  100  in  each  case. 

Table  36.  —  Relative  Effectiveness  of  Nitrogenous   Ferti- 


Nitrogen  Carriers 


Nitrate  of  soda   .     . 
Sulfate  of  ammonia 
Dried  blood    .     .     . 
Bone  meal 
Stable  manure    .     . 
Tankage    .... 
Horn-and-hoof  meal 
Linseed  meal       .     . 
Cottonseed  meal 
Castor  pomace    . 
Wool  waste    .     .     . 
Leather  meal       .     . 
Dry  ground  fish 


Wagner 

Johnson 

and 

and 

Dorsch 

Others 

100 

100 

90 

70 

73 

60 

17 

45 

49 

70 

68 

69 

65 

65 

30 

20 

64 

Voorhees 

AND 
LlPMAN 


100 
70 
64 

53 


While  these   experiments  are   helpful  in  giving  an  idea 
of  the  relative  values  of  these  fertilizers,  they  do  not  necessa- 


168  SOILS   AND   FERTILIZERS 

rily  hold  for  every  soil.  It  will  be  noticed  that  there  is  con- 
siderable discrepancy  in  these  results,  but  that  is  always  to 
be  expected.  A  fertilizer  may  have  a  more  rapid  rate  of  am- 
monification  or  nitrification  than  another  fertilizer  in  one 
soil  and  less  rapid  in  another  soil. 

219.  Relative  values  of  organic  and  inorganic  nitrogenous 
fertilizers.  —  In  the  experiments  cited  the  organic  fertilizers 
were,  in  every  case,  less  effective  than  the  inorganic  ones. 
However,  the  cost  of  a  pound  of  nitrogen  is  generally  more  in 
the  better  class  of  organic  fertilizers,  like  dried  blood,  than  it 
is  in  the  inorganic  fertilizers,  like  nitrate  of  soda  and  sulfate 
of  ammonia.  This  may  be  because  of  the  demand  of  fer- 
tilizer manufacturers  for  a  dry  material  for  their  goods,  but 
the  beneficial  effect  of  the  organic  matter  it  contains  may 
also  be  a  factor  in  creating  the  demand  for  dried  blood. 

QUESTIONS 

1.  Name  the  forms  in  which  nitrogen  occurs  in  soils. 

2.  State  what  forms  of  nitrogen  are  absorbed  by  crops,  and  what 
differences  exist  between  plants  in  this  respect. 

3.  Name  the  fertilizer  materials  that  contain  nitrogen,  and  spec- 
ify the  form  in  which  nitrogen  occurs  in  each. 

4.  What  crops  are  particularly  benefited  by  nitrate  fertilizers  ? 

5.  How  is  the  nitrogen  of  nitrate  and  ammonia  fertilizers  likely 
to  be  lost  from  soils,  especially  if  no  crop  is  on  the  land  ? 

6.  How  may  danger  arising  from  formation  of  poisonous  products 
in  the  decomposition  of  cyanamid  be  avoided  ? 

7.  Describe  the  effects  of  nitrogen  on  plant  growth. 

8.  State  the  order  of  availability  of  nitrogen  in  nitrate  of  soda, 
sulfate  of  ammonia  and  dried  blood. 

LABORATORY   EXERCISES 

Exercise  I.  —  In  Exercise  V,  Chapter  I,  an  experiment  designed 
to  show  the  importance  of  the  plant-food  materials  to  plant  growth 
was  described.  If  this  test  has  been  properly  conducted  the  influ- 
ence of  nitrogen  upon  plant  growth  will  be  clearly  shown. 


NITROGENOUS    FERTILIZERS  169 

Exercise  II.  —  Examination  and  identification  of  nitrogen 
fertilizers. 

Materials.  —  Set  of  fertilizers  (comprising  sodium  nitrate,  am- 
monium sulfate,  cyanamid,  dried  blood  and  tankage),  evaporating 
dish,  phenoldisulphonic  acid,  ammonia,  funnel  and  filter  paper, 
litmus  paper,  hand  lens,  flame. 

Procedure.  —  It  is  well  for  the  student  to  be  able  to  identify 
the  common  fertilizers  and  to  know  a  few  practical  tests  when  the 
identity  is  in  doubt.  The  following  outline  is  given  with  this  end 
in  view. 

Sodium  Nitrate 

This  fertilizer  appears  in  clouded  light  yellowish  crystals,  soluble 
in  water  and  rather  deliquescent.     It  has  no  marked  odor. 

Hold  a  crystal  in  the  flame.  Note  the  brilliant  yellow  color. 
This  is  a  test  for  the  element  sodium. 

Test  for  the  nitrate  part  of  the  fertilizer  by  moistening  a  crystal 
in  an  evaporating  dish  with  a  drop  of  phenoldisulphonic  acid. 
Allow  to  stand  a  few  minutes  and  then  dissolve  in  a  little  water. 
Now  neutralize  with  ammonia  and  obtain  the  yellow  color  charac- 
teristic of  nitrates. 

Ammonium  Sulfate 

This  fertilizer  is  a  light  grayish  colored  salt,  finely  ground  and 
soluble  in  water.  Heat  a  little  in  an  evaporating  dish  and  note  the 
odor  of  ammonia. 

Cyanamid 

Cyanamid  is  a  fine,  dry,  black  powder  which  carries  besides  its 
nitrogen  compound,  carbon  and  lime.  The  carbon  may  be  tested 
for  by  rubbing  the  fertilizer  between  the  fingers.  Dissolve  as  much 
of  the  fertilizer  as  possible  in  water,  filter  and  test  the  filtrate  with 
litmus  paper.  It  should  be  intensely  alkaline  on  account  of  the 
lime  it  contains.  The  physical  characters  of  the  fertilizer  are  such 
as  to  make  it  easily  recognized. 

Dried   Blood  and   Tankage 

These  materials  can  be  easily  identified  and  distinguished  by 
their  physical  properties,  especially  if  a  hand  lens  is  used.  Consid- 
erable hair  and  bone  is  likely  to  be  found  in  tankage.  The  odor  of 
both  is  characteristic.  Study  each  fertilizer  until  identification  is 
easy. 


170  SOILS   AND   FERTILIZERS 

Exercise  III.  —  Comparison  of  fertilizer  effects  on  plant 
growth. 

Materials.  —  Fertilizers,  flower  pots,  poor  sandy  soil,  oat  seed. 

Procedure.  —  It  may  be  of  advantage  to  compare  two  or  more 
of  the  nitrogen  fertilizers  with  reference  to  their  effect  on  plant 
growth.  Fill  flower  pots  with  the  same  amount  of  a  poor 
sandy  loam  after  thoroughly  mixing  the  fertilizer  with  the  soil. 
Apply  nitrogen  fertilizers  at  the  rate  of  250  pounds  per  acre  (1  of 
fertilizer  to  1 0,000  of  soil) .  Also  add  at  the  same  time  acid  phosphate 
and  muriate  of  potash  at  the  rate  of  1  to  5000  of  soil  respectively. 
One  gram  of  lime  per  pot  is  also  necessary.  Leave  one  pot  untreated 
with  the  nitrogen  fertilizers  as  a  check.  Now  plant  oat  seeds  and 
bring  the  soil  to  optimum  moisture  content.  When  seedlings  are 
a  week  old  thin  to  proper  number.  Keep  pots  in  suitable  place  and 
observe  relative  development  of  the  plants  under  the  different  treat- 
ments. 


CHAPTER  XII 
PHOSPHORIC  ACID  FERTILIZERS 

Fertilizers  commonly  used  in  this  country  for  their  phos- 
phoric acid  may  be  divided  into  two  classes,  natural  phos- 
phate fertilizers  and  acid  phosphate  fertilizers.  The  former 
are  in  the  condition  in  which  they  are  found  in  nature,  and 
are  very  difficultly  soluble.  The  latter  are  merely  the  phos- 
phate fertilizers  that  have  been  treated  with  strong  acid, 
after  which  process  they  are  readily  available  to  plants. 
There  is  an  intermediate  form  present  in  basic  slag,  which  is 
not  quite  so  available  as  the  acid  phosphate,  but  more 
readily  available  than  the  natural  phosphate  fertilizers. 
Natural  phosphates,  when  in  organic  compounds,  like  bone, 
are  more  readily  available  than  when  in  purely  inorganic 
compounds,  like  rock. 

220.  Bone  phosphate.  —  Most  of  the  bone  now  used  in 
fertilizers  has  been  steamed  or  boiled,  which  removes  the  fat, 
and  also  the  nitrogen  that  fresh  bones  contain.  Fresh  bones 
have  a  content  of  about  22  percent  phosphoric  acid  and 
4  percent  nitrogen.  .  Steamed  bones  have  from  28  to  30  per- 
cent phosphoric  acid  and  1.5  percent  nitrogen.  Bone  tankage, 
which  has  already  been  spoken  of  as  a  nitrogenous  fertilizer, 
contains  from  7  to  9  percent  of  phosphoric  acid.  Bone  should 
always  be  finefy  ground,  as  it  is  then  more  readily  available. 
It  is  a  slow  acting  form  of  phosphoric  acid. 

221.  Mineral  phosphates.  —  These  are  found  as  natural 
deposits  of  rock  in  various  parts  of  the  world,  some  of  the 

171 


172  SOILS   AND   FERTILIZERS 

most  extensive  being  in  the  United  States.  When  ground 
these  are  often  called  "  floats."  South  Carolina  phosphate 
contains  from  26  to  28  percent  of  phosphoric  acid.  Florida 
phosphate  exists  in  the  forms  of  soft  phosphate,  pebble  phos- 
phate and  boulder  phosphate.  Soft  phosphate  contains  from 
18  to  30  percent  phosphoric  acid,  and  because  of  its  being 
more  easily  ground  than  most  of  these  rocks  it  is  often  applied 
to  the  land  without  being  first  converted  into  an  acid  phos- 
phate. The  other  two  forms,  pebble  phosphate  and  boulder 
phosphate,  are  highly  variable  in  composition,  varying  from 
20  to  40  percent  in  phosphoric  acid  content. 

Tennessee  phosphate  contains  from  30  to  35  percent  of  phos- 
phoric acid.  In  addition  to  these  deposits,  which  have  been 
extensively  mined  since  their  discovery,  there  have  been  found 
much  larger  deposits  in  the  states  of  Idaho,  Wyoming  and 
Montana,  but  these  have  not  yet  been  worked. 

Apatite  and  coprolites  are  other  forms  of  natural  phosphate 
that  are  used  as  fertilizers.  The  former  is  found  in  Canada 
and  the  latter  in  England  and  France.  They  are  not  of  much 
importance  in  the  fertilizer  business  of  this  country. 

222.  Basic  slag.  —  This  is  also  called  Thomas  phosphate. 
It  is  a  by-product  in  the  manufacture  of  steel  from  pig  iron 
rich  in  phosphorus.  The  phosphoric  acid  in  this  material  is 
more  readily  available  than  that  in  the  mineral  phosphates, 
and  when  used  as  a  fertilizer  it  does  not  require  treatment 
with  acid.  It  should  be  finely  ground.  It  is  not  extensively 
used  in  the  United  States. 

223.  Acid  phosphate.  —  The  very  difficultly  soluble  phos- 
phates may  be  rendered  more  easily  soluble  by  treatment 
with  sulfuric  acid.  The  product  is  called  acid  phosphate. 
When  applied  to  soils  it  is  much  more  available  to  plants 
than  are  any  of  the  natural  phosphates.  Acid  phosphates 
contain  gypsum  or  land  plaster  as  well  as  phosphoric  acid. 
The  proportion  of  the  total  quantity  of  phosphoric  acid 


PHOSPHORIC  ACID   FERTILIZERS  173 

originally  present  that  is  rendered  soluble  depends  on  the 
quantity  of  sulfuric  acid  added.  In  practice  there  is  usually 
part  of  the  phosphoric  acid  that  is  left  in  an  insoluble  form. 

224.  Composition  of,  acid  phosphate.  —  Acid  phosphate 
made  from  animal  bone  is  called  dissolved  bone  and  contains 
about  12  percent  of  available  and  from  3  to  4  percent  of 
insoluble  phosphoric  acid.  It  also  contains  some  nitrogen. 
When  made  from  South  Carolina  rock,  acid  phosphate  con- 
tains from  12  to  14  percent  of  available  phosphoric  acid, 
including  from  1  to  3  percent  of  what  is  called  reverted 
phosphoric  acid.  The  best  Florida  acid  phosphate  contains 
as  high  as  17  percent,  and  the  Tennessee  acid  phosphate  14 
to  18  percent  of  available  phosphoric  acid. 

225.  Reverted  phosphoric  acid.  —  A  change  sometimes 
occurs  in  acid  phosphate  on  standing,  by  which  some  of  the 
phosphoric  acid  becomes  less  easily  soluble,  and  to  that  extent 
the  value  of  the  fertilizer  is  lessened.  This  change  is  known 
as  reversion.  It  is  much  more  likely  to  occur  in  acid  phos- 
phate made  from  rock  than  in  that  made  from  bone.  The 
quality  of  the  material  affects  this  change.  The  presence  of 
iron  and  aluminum  is  supposed  to  increase  reversion.  Re- 
verted phosphoric  acid  is  probably  not  so  available  as  the 
original  acid  phosphate. 

226.  Absorption  of  acid  phosphate  by  soil.  —  Like  many 
soluble  substances  acid  phosphate,  when  applied  to  soil, 
is  in  part  absorbed  and  held  in  a  form  in  which  it  will  not  be 
leached  out  by  the  drainage  water,  but  on  the  other  hand, 
remains  in  a  condition  in  which  it  is  available  to  plants. 
Part  of  the  soluble  phosphoric  acid  may  unite  with  iron  or" 
aluminum  in  the  soil  to  form  insoluble  combinations.  The 
richer  a  soil  is  in  lime  the  less  is  the  danger  of  forming  these 
insoluble  combinations.  The  availability  of  acid  phosphate 
may  continue  for  a  second  year,  or  even  longer,  after  being 
applied  to  the  soil. 


174  SOILS   AND   FERTILIZERS 

227.  Relative   availability  of  phosphoric  acid  fertilizers. 

—  The  availability  of  these  fertilizers  has  been  casually  men- 
tioned as  each  was  discussed,  but  a  brief  resume  will  serve 
to  make  the  matter  more  definite.  Acid  phosphate,  including 
dissolved  bone,  is  the  most  readily  available  of  the  phos- 
phoric acid  fertilizers.  The  reverted  portion  is  more  or  less 
available,  depending  on  the  character  of  the  original  rock, 
and  on  the  kind  of  soil  to  which  it  is  applied.  It  is  not  as 
valuable  as  the  soluble  phosphoric  acid.  The  insoluble  por- 
tion has  no  greater  availability  than  the  rock  from  which  the 
acid  phosphate  was  made. 

Next  to  acid  phosphate  in  availability  comes  basic  slag, 
then  steamed  bone  and  finally  the  rock  phosphates. 

Acid  phosphate  and  basic  slag  may  be  used  for  top  dressing 
grass  or  winter  grains,  but  the  other  fertilizers  must  be  in- 
corporated in  the  soil  in  order  to  become  available.  It  is 
necessary  that  they  shall  be  acted  on  by  the  soil  water  having 
carbon  dioxide  in  solution  and  possibly  by  other  acids  formed 
by  the  decomposition  of  organic  matter. 

228.  Rock  phosphate  versus  acid  phosphate.  —  The  ques- 
tion has  frequently  been  raised  in  the  last  few  years  regarding 
the  use  of  ground  rock  phosphate  or  floats  as  a  substitute  for 
acid  phosphate.  Which  of  these  practices  is  the  better  must 
be  largely  determined  by  practical  experiment,  and  by  a  study 
of  the  conditions  under  which  floats  become  available. 

It  is  urged  in  favor  of  floats  that  the  price  of  phosphoric  acid 
is  much  less  in  this  form  than  in  the  form  of  acid  phosphate, 
which  is  made  by  a  more  or  less  expensive  process.  It  is 
further  argued  that  even  if  much  more  material  must  be  used 
in  order  to  get  a  pound  of  available  phosphoric  acid  the  re- 
mainder stays  in  the  soil  to  increase  the  total  supply,  and  that 
gradually  it  will  become  available,  finally  perhaps  reaching 
a  point  where  no  more  need  be  applied. 

On  the  other  side  is  the  well-established  practice  of  using 


PHOSPHORIC  ACID   FERTILIZERS  175 

acid  phosphate,  which  dates  back  more  than  half  a  century, 
and  has  been  accepted  during  that  time  as  an  improvement 
over  the  use  of  untreated  bone,  which  was  largely  super- 
seded when  the  process  of  making  acid  phosphate  was  in- 
vented. 

On  most  soils  acid  phosphate  apparently  gives  the  more 
profitable  immediate  returns.  On  some  of  the  rich  soils  of 
the  Middle  West,  however,  there  is  an  indication  that 
ground  rock  is  a  more  economical  source  of  phosphoric  acid. 
Except  in  those  regions  where  the  superiority  of  floats  has 
been  demonstrated  it  is  probably  safer  to  use  acid  phosphate. 

229.  Effect  of  phosphoric  acid  on  plant  growth.  —  As  has 
been  previously  stated,  phosphoric  acid  is  essential  to  the 
growth  of  plants.  It  is  absorbed  by  plants  at  a  fairly  uniform 
rate  throughout  the  period  of  their  active  growth,  while  nitro- 
gen is  largely  taken  up  during  the  early  stages  of  growth. 
Nitrogen  and  phosphoric  acid  are  closely  associated  in  plant 
development. 

One  very  apparent  effect  of  phosphoric  acid  is  to  hasten 
ripening.  Cereal  plants  that  receive  an  ample  supply  of 
avail  able  phosphoric  acid  reach  the  heading  stage  and  final 
maturity  sooner  than  do  plants  having  an  insufficient  supply. 
This  may  be  an  advantage  in  a  climate  having  a  cool  short 
season  as  it  may  help  the  crop  to  avoid  frost  in  the  fall.  On 
the  other  hand  this  rapid  ripening  may  limit  the  yield 
in  a  dry  season,  when  there  is  a  tendency  for  the  crop  to 
shorten  its  growing  periods  sufficiently  to  curtail  the  quan- 
tity of  nutrients  it  absorbs  and  the  food  it  elaborates. 

Root  development  is  always  stimulated  by  available  phos- 
phoric acid.  Young  plants  send  their  roots  more  deeply 
into  the  soil,  which  is  an  advantage  in  dry  regions,  where  the 
top  soil  dries  out  quickly.  Under  any  circumstances  it  in- 
creases the  absorbing  surfaces  and  benefits  growth. 

The  quality  of  many  crops,  particularly  of  pastures,  is 
improved  by  phosphoric  acid.     Animals  reared  on  pastures 


176  SOILS   AND    FERTILIZERS 

fertilized  with  phosphoric  acid  have  been  found,  in  a  number 
of  experiments  conducted  in  Great  Britain,  to  be  more  vigor- 
ous and  to  develop  faster  than  when  no  phosphoric  acid  was 
applied. 

By  balancing  the  effect  of  nitrogen,  phosphoric  acid  pre- 
vents an  undue  formation  of  straw,  at  the  same  time  making 
it  stronger ;  on  the  other  hand,  it  increases  the  production  of 
grain  in  cereal  crops.  In  the  same  way  it  increases  resistance 
to  disease,  probably  by  producing  a  more  normal  develop- 
ment of  the  plant  cells. 

An  insufficient  supply  of  phosphoric  acid  is  less  easy  to  de- 
tect than  is  an  inadequate  supply  of  nitrogen,  because  its  ef- 
fect is  exercised  on  the  production  of  grain  or  other  seeds, 
rather  than  on  the  height  and  color  of  the  plants.  It  re- 
quires some  care,  therefore,  to  detect  a  lack  of  phosphoric 
acid.  * 

230.  Plants  particularly  benefited  by  phosphoric  acid.  — 
The  crops  that  respond  particularly  well  to  applications  of 
phosphoric  acid  are  turnips,  barley,  cabbage  and  other  plants 
of  that  family,  beets,  spinach,  radishes  and  lettuce.  Corn  is 
said  to  be  well  qualified  to  secure  its  phosphoric  acid  from  the 
natural  phosphates,  as  are  also  some  of  the  legumes. 

QUESTIONS 

1.  Name  the  natural  phosphate  fertilizers. 

2.  Why  should  natural  phosphates  be  finely  ground,  when  ap- 
plied to  the  soil  ? 

3.  How  does  basic  slag  compare  in  availability  with  rock  phos- 
phate ? 

4.  How  is  acid  phosphate  made,  and  how  does  it  compare 
in  availability  with  the  natural  phosphates  ? 

5.  What  is  reverted  phosphoric  acid  ? 

6.  Why  is  soluble  phosphoric  acid  not  readily  leached  out  of  soil 
after  being  applied  as  a  fertilizer  ? 

7.  What  phosphoric  acid  fertilizers  may  be  used  for  top  dressing 
grass  or  other  crops  ? 


PHOSPHORIC  ACID   FERTILIZERS  111 

8.  Compare  floats  and  acid  phosphate  as  sources  of  phosphoric 
acid  when  fertilizing  land. 

9.  Describe  the  effects  of  phosphoric  acid  on  plant  growth. 

10.  Name  the  plants  that  are  particularly  benefited  by  fertili- 
zation with  phosphoric  acid. 

LABORATORY   EXERCISES 

Exercise  I.  —  In  Exercise  V,  Chapter  I,  an  experiment  was 
described  that  was  designed  to  show  the  importance  of  some  plant- 
food  materials  to  plant  growth.  If  this  test  has  been  properly  con- 
ducted it  should  now  be  ready  to  show  the  actual  effects  of  the 
phosphoric  acid  on  crop  development. 

Exercise  II.  —  Examination  and  identification  of  phosphate 
fertilizers. 

Materials.  —  Set  of  fertilizers  (consisting  of  ground  bone,  raw 
rock  phosphate,  basic  slag  and  acid  phosphate),  hydrochloric  acid, 
nitric  acid,  litmus  paper,  flame,  test  tubes,  funnel  and  filter  paper, 
ammonium  molybdate  solution. 

The  ammonium  molybdate  solution  is  made  as  follows  : 
Dilute  50  c.c.  of  ammonia  (sp.  gr.  .9)  with  75  c.c.  of  distilled  water. 
Dissolve  in  this  25  grams  of  molybdic  acid.  Pour  this  into  a  solu- 
tion consisting  of  175  c.c.  of  nitric  acid  (sp.  gr.  1.42)  diluted  with 
250  c.c.  of  water.  Make  the  addition  slowly  with  constant  stirring. 
Allow  to  stand  in  a  warm  place  for  two  days  and  then  decant  the 
clear  supernatant  liquid  for  use. 

Procedure.  —  The  fertilizers  should  be  tested  as  described  below 
and  examined  until  their  identification  is  easy  and  positive. 

Ground  Bone     ■ 
Bone  is  usually  ground  to  a  coarse  powder.     It  is  dry  and  has  a 
decided  and  characteristic  odor.     It  is  light  gray  in  color,  insoluble 
in  water  and  has  a  characteristic  appearance  under  the  hand  lens. 
Its  physical  characters  are  sufficient  for  identification. 

Ground   Phosphate  Rock 

Floats  appear  on  the  market  as  a  light  gray  powder,  insoluble 
in  water  and  with  little  odor. 

Dissolve  a  small  amount  in  hydrochloric  acid,  heat  and  filter.  Add 
ammonia  until  a  precipitate  appears.  Dissolve  it  with  a  small 
amount  of  nitric  acid.  Then  add  ammonium  molybdate.  Heat  gen- 
tly.   A  yellow  precipitate  indicates  the  presence  of  phosphoric  acid. 

N 


178  SOILS   AND   FERTILIZERS 

Basic  Slag 

This  form  of  phosphoric  acid  appears  as  a  dry,  dark  gray  powder 
with  a  slight  odor.  If  differs  from  cyanamid  in  that  it  does  not 
stain  the  fingers  upon  handling.     It  is  alkaline  to  litmus  paper. 

Test  for  phosphates  as  under  phosphate  rock. 

Acid   Phosphate 

This  fertilizer  is  a  slightly  deliquescent  salt,  brownish  gray  in 
color,  and  finely  ground.  Its  odor  is  characteristic  and  serves  to 
distinguish  it  from  ground  rock.  Unlike  floats  it  is  partially  soluble 
in  water. 

Dissolve  a  small  amount  in  water.  Filter  and  test  the  filtrate  for 
phosphoric  acid  as  described  above. 

Exercise  III.  —  Comparison  of  fertilizer  effects  on  plant 
growth. 

Materials.  —  Fertilizers,  flower  pots,  poor  sandy  soil,  oat  seed. 

Procedure.  —  The  comparison  of  the  various  phosphorus  fer- 
tilizers upon  crop  growth,  especially  acid  phosphate  and  raw  rock,  is 
a  valuable  experiment.  Fill  the  required  number  of  flower  pots 
with  the  same  amount  of  a  poor  sandy  loam  after  thoroughly 
mixing  the  fertilizer  with  the  soil.  Apply  the  phosphorus  ferti- 
lizers at  the  rate  of  250  pounds  per  acre  (1  of  fertilizer  to  10,000 
of  soil).  Also  add  at  the  same  time  sodium  nitrate  and  muriate 
of  potash  at  the  rate  of  1  of  fertilizer  to  5000  of  soil  respectively. 
Apply  one  gram  of  lime  per  pot.  Leave  one  pot  untreated  with  the 
phosphorus  fertilizers  as  a  check. 

Now  plant  the  oat  seed  and  raise  the  soil  to  optimum  moisture. 
When  seedlings  are  a  week  old,  thin  to  required  number.  Keep 
pots  under  suitable  conditions  and  observe  relative  development  of 
the  various  treatments. 


CHAPTER  XIII 
POTASH  AND  SULFUR  FERTILIZERS 

The  materials  used  as  potash  fertilizers,  with  a  very 
few  exceptions,  are  soluble  in  water.  The  matter  of  their 
relative  availability  is,  therefore,  of  minor  importance. 
When  applied  to  soil,  the  potash  salts  are  absorbed  and  held 
in  a  condition  in  which  they  leach  out  only  in  moderate  quan- 
tities, but  to  a  greater  extent  than  does  phosphoric  acid.  In 
the  absorbed  condition,  however,  they  are  readily  available 
to  plants. 

It  seems  strange  that  with  the  many  thousand  pounds  of 
potash  contained  in  an  acre  of  ordinary  land,  as  may  be/ 
seen  by  consulting  Table  17,  there  should  be  any  benefit 
derived  from  the  few  pounds  of  potash  that  are  contained 
in  a  fertilizer.  The  fact  that  the  fertilizer  is  effective  gives 
emphasis  to  two  facts :  (1)  the  great  insolubility  of  the 
soil  potash ;   (2)  the  availability  of  the  absorbed  potash. 

231.  Stassfurt  salts.  —  Most  of  the  potash  fertilizers  used 
in  the  United  States  come  from  Germany,  where  there  are 
extensive  beds  varying  from  50  to  150  feet  in  thickness,  lying 
under  a  region  of  country  extending  from  the  Harz  mountains 
to  the  Elbe  river  and  known  as  the  Stassfurt  deposits. 

*  There  are  two  forms  in  which  potash  is  found  in  the  Stass- 
furt beds.  These  are  the  sulfate  of  potash  and  the  muriate 
of  potash.  It  is  necessary  to  distinguish  between  these  two 
because  the  muriate,  when  used  in  large  applications,  has  an 
injurious  effect  on  certain  crops,  among  which  are  tobacco, 

179 


180  SOILS   AND   FERTILIZERS 

sugar  beets  and  potatoes.  On  cereals,  legumes  and  grasses 
the  muriate  may  be  used  without  causing  any  injury,  provided 
it  is  not  brought  in  contact  with  the  seed. 

Comparatively  pure  forms  of  both  muriate  and  sulfate  of 
potash  are  on  the  market.  The  former  contains  about  50 
percent  of  potash,  and  the  latter  about  48  to  50  percent.  The 
sulfate  is  more  expensive,  but  the  muriate  is  equally  good, 
except  on  the  rather  small  number  of  crops  that  are  injured 
by  it.    . 

The  mineral  produced  in  largest  quantity  by  the  Stass- 
furt  mines  is  kainit,  consisting  of  sulfate  of  potash  and 
muriate  of  magnesia.  It  contains  from  12  to  20  percent 
of  potash.  It  has  the  same  effect  on  crops  as  has  the  muri- 
ate of  potash. 

Kainit  should  not  be  drilled  with  the  seed  of  any  crop 
for  when  placed  in  direct  contact  with  the  seed  injury 
may  result.  It  is  a  wise  precaution  to  apply  the  kainit  a 
week  or  more  before  planting,  if  a  heavy  application  is  to 
be  made. 

232.  Wood  ashes.  —  The  principal  supply  of  potash  in  this 
country  at  one  time  was  wood  ashes.  With  the  diminished 
consumption  of  wood  as  fuel,  this  source  of  potash  has  fallen 
off.  Now  wood  ashes  are  only  an  occasional  supply.  In 
addition  to  potash,  wood  ashes  furnish  considerable  lime*  and 
a  little  phosphoric  acid„  There  is  no  muriate  present  and 
hence  no  injurious  effect  on  plants,  but  it  should  not  be 
brought  directly  in  contact  with  seeds. 

Unleached  wood  ashes  contain  5  to  6  percent  of  potash, 
2  percent  of  phosphoric  acid  and  30  percent  of  lime.  Leached 
wood  ashes  have  only  about  1  percent  of  potash,  1^  percent 
of  phosphoric  acid  and  28  to  29  percent  of  lime.  The  un- 
leached ashes  are  the  more  valuable. 

Wood  ashes  are  not  only  an  excellent  potash  fertilizer, 
but  are  also  useful  to  counteract  acidity  in  soils,  for  which 


POTASH   AND   SULFUR   FERTILIZERS  181 

purpose  the  lime  in  the  ashes  is  even  more  effective  than  the 
potash  because  there  is  more  of  it. 

233.  Insoluble  potash  fertilizers.  —  Many  rocks  contain 
potash ;  for  this  reason  there  is  a  large  quantity  in  soils.  It 
has  been  proposed  to  grind  the  rocks  that  are  richest  in  pot- 
ash and  to  use  them  for  fertilizer.  Experiments  with  finely 
ground  feldspar  have  been  conducted  by  a  number  of  investi- 
gators, but  have  given  little  encouragement  for  the  successful 
use  of  this  material.  An  insoluble  form  of  potash  is  not 
given  any  value  in  the  rating  of  a  fertilizer. 

234.  Effects  of  potash  on  plant  growth.  —  Plants  require 
potash  in  order  to  make  a  normal  growth.  If  no  available 
potash  is  present,  the  elaboration  of  sugar  and  starch  in 
plants  is  curtailed"^  Crops  like  potatoes  and  sugar  beets,  that 
produce  much  starch  and  sugar,  are  greatly  benefited  by  an 
abundant  supply  of  potash.  It  also  has  other  functions  in 
plants  that  make  it  indispensable.  The  grain  of  cereals  fills 
out  better  and  weighs  more  to  the  bushel  and  the  straw  is 
stronger,  when  a  good  supply  of  potash  is  available.  Leg- 
umes are  usually  greatly  benefited  by  potash.  The  large 
formation  of  sugar  and  starch  affords  the  nitrogen-fixing 
bacteria  the  kind  of  food  which  they  need,  and  to  obtain 
which  they  live  in  symbiosis  with  the  legume.  If  part  of 
a  clover  and  timothy  field  be  well  fertilized  with  potash, 
and  another  part  receive  none,  it  is  likely  to  be  the  case  that 
the  proportion  of  clover  to  timothy  will  be  much  greater  on 
the  fertilized  part  of  the  field  than  on  the  unfertilized  part, 
unless  the  natural  supply  of  available  potash  is  unusually 
large. 

Potash  tends  to  delay  ripening  of  plants,  but  not  to  the 
same  extent  as  does  nitrogen.  It  also  has  an  influence 
similar  to  that  of  phosphoric  acid,  in  that  it  helps  to  overcome 
the  tendency  of  nitrogen  to  make  plants  less  resistant  to  dis- 
ease. 


182  SOILS   AND   FERTILIZERS 

235.  Sulfur  as  a  fertilizer.  —  It  has  been  pointed  out  that 
sulfur  is  one  of  the  substances  essential  to  plant  growth, 
but  it  has  generally  been  considered  that  a  sufficient  quantity 
is  contained  in  arable  soils  to  supply  the  needs  of  crops, 
and  that  its  application  as  a  fertilizer  is  unnecessary.  In 
spite  of  this  there  have  been  occasional  experiments  con- 
ducted from  time  to  time  in  which  sulfur,  usually  in  the  form 
of  flowers  of  sulfur,  has  been  applied  to  soils  to  ascertain  its 
effect  on  plant  growth. 

236.  Experiments  with  sulfur  as  a  fertilizer.  —  Most  of 
the  experiments  with  sulfur  have  been  conducted  in  Europe. 
In  some  cases  the  application  of  sulfur  to  the  soil  was  found  to 
be  beneficial  to  plant  growth,  in  other  cases  there  was  no  ef- 
fect. Where  no  result  was  produced,  it  is  reasonable  to  be- 
lieve that  there  was  sufficient  sulfur  in  the  soil  to  supply 
the  needs  of  the  plants,  and  that  any  further  addition  was  un- 
necessary. In  those  experiments  in  which  sulfur  was  found 
to  exert  a  beneficial  action  we  cannot  be  certain  that  the  in- 
creased plant  growth  was  due  to  the  larger  quantity  of  sulfur 
obtained  by  the  plants.  Sulfur  has  been  found  to  influence 
the  action  of  the  germs  in  soils,  and  it  is  possible  that  the 
plants  grew  better  because  the  soil  nitrogen  was  converted 
more  rapidly  into  an  available  form  by  the  stimulating  ef- 
fect of  sulfur  on  the  bacteria  concerned  in  that  process.  Sul- 
fur sometimes  has  other  beneficial  effects  on  plant  growth. 
These  secondary  reactions  sometimes  lead  to  erroneous  con- 
clusions regarding  the  effect  of  a  fertilizer. 

237.  Quantity  of  sulfur  contained  in  crops.  —  It  has  been 
computed  from  the  analyses  of  various  plants  that  the 
quantity  of  sulfur,  when  figured  as  sulfur  trioxide,  that  is 
removed  from  the  soil  by  crops  of  ordinary  size  is  sometimes 
greater,  and  sometimes  less,  depending  on  the  kind  of  crop, 
than  is  the  quantity  of  phosphoric  acid  removed  by  the  same 
crop.     This  may  be  seen  in  the  following  table. 


POTASH   AND  SULFUR   FERTILIZERS 


183 


Table  37.  —  Pounds  op  Sulfur  Trioxide  and  Phosphoric  Acid 
Removed  from  an  Acre  of  Soil  by  Average  Crops 


Content  in  Pounds  to  the 
Acre 


Crop  and  Yield  to  the  Acre 


Wheat  (30  bu.) 

Barley  (40  bu.) 

Oats  (45  bu.) 

Corn  (30  bu.) 

Alfalfa  (9000  lb.  dry  wt.) 
Turnips  (4657  lb.  dry  wt.)      . 
Cabbage  (4800  lb.  dry  wt.)    . 
Potatoes  (3360  lb.  dry  wt.)    . 
Meadow  hay  (2822  lb.  dry  wt.) 


21.1 
20.7 
19.7 
18.0 
39.9 
33.1 
61.0 
21.5 
12.3 


238.  Quantities  of  sulfur  in  soils.  —  Analyses  of.  virgin 
and  cultivated  soils  have  shown  that  there  has  been  a  de- 
pletion of  sulfur  in  cropped  soils.  It  also  appears  that  the 
quantity  of  sulfur  trioxide  is  probably  not  greater  than  the 
quantity  of  phosphoric  acid  in  many  soils,  as  may  be  seen 
from  the  following  table,  which  is  based  on  the  analyses  of  a 
considerable  number  of  soils. 

Table  38.  —  Pounds  of  Sulfur  Trioxide  and  Phosphoric  Acid 
in  Sandy  and  Clay  Soils 


Pounds  per  Acre 

Sulfur  Trioxide 

Phosphoric  Acid 

Sandy  soils 

Clay  soils 

1650 
2250 

2610 
4230 

239.  Quantities  of  sulfur  in  drainage  water.  —  Sulfur 
suffers  a  much  greater  removal  in  drainage  water  than  does 
phosphoric  acid.     In  lysimeter  experiments  this  has  been 


184 


SOILS   AND   FERTILIZERS 


shown  to  amount  to  from  31  to  56  pounds  to  an  acre  in  one 
year,  depending  on  whether  the  soil  was  limed  or  unlimed, 
cropped  or  bare,  as  shown  in  the  following  table. 


Table  39.  —  Pounds  of  Sulfur  in  Drainage  Water  from  One 
Acre  of  Soil 


Sulfur 

Treatment 

Crops  Grown 

(Pounds  per 
Acre) 

Lime 

Fertilizer 

1910 

1911 

1912 

1913-14 

1911- 
14 

Annual 
Aver- 
age 

None 

None 

Maize 

Oats 

Wheat 

Timothy 

127.2 

31.8 

None 

None 

None 

None 

None 

None 

176.1 

44.0 

None 

None 

Maize 

Oats 

Wheat 

Timothy  and  clover 

126.2 

31.5 

None 

None 

Maize 

Oats 

Grasses 

Grasses 

172.8 

43.2 

Lime 

None 

Maize 

Oats 

Wheat  ' 

Timothy 

175.7 

43.9 

Lime 

None 

None 

None 

None 

None 

212.6 

53.1 

Lime 

None 

Maize 

Oats 

Wheat 

Timothv  and  clover 

164.2 

41.0 

Lime 

None 

Maize 

Oats 

Grasses 

Grasses 

151.0 

37.7 

None 

Sulfate  of  potash 

Maize 

Oats 

Wheat 

Timothy 

225.7 

56.4 

Lime 

Sulfate  of  potash 

Maize 

Oats 

Wheat 

Timothy 

248.1 

62.0 

With  the  rather  large  removal  of  sulfur  in  crops  and  drain- 
age water,  and  a  somewhat  meager  supply  in  the  soil,  it  would 
appear  likely  that  a  deficiency  might  ultimately  arise  if  there 
were  no  way  in  which  sulfur  could  be  added  to  soils.  To 
offset  the  loss  there  is  a  certain  quantity  of  sulfur,  amounting 
to  6  or  8  pounds  an  acre,  washed  down  by  the  rainfall  each 
year.  There  is  also  a  variable  quantity  of  sulfur  contained 
in  some  of  the  commonly  used  fertilizers. 

240.  Sulfur  containe4  in  fertilizers.  —  It  has  been  rather 
fortunate  perhaps  that  many  of  the  fertilizers  that  are  used 
because  they  contain  other  plant-food  materials,  also  con- 
tain sulfur.  This  is  true  of  farm  manure  and  other  animal 
and  bird  excrements,  residues  of  crops,  animal  offal,  gypsum 
or  land  plaster,  acid  phosphate,  sulfate  of  ammonia,  kainit, 
sulfate  of  potash  and  all  the  slaughter  house  products. 


POTASH   AND   SULFUR   FERTILIZERS  185 

Whether,  under  ordinary  methods  of  farming,  it  is  desir- 
able to  use  any  fertilizer  for  the  sulfur  it  contains  has  not  yet 
been  ascertained.  It  would  appear,  however,  to  be  a  subject 
worthy  of  consideration. 

QUESTIONS 

1.  What  occurs  to  a  soluble  potash  fertilizer  when  applied  to 
soil? 

2.  With  thousands  of  pounds  of  potash  in  an  acre  of  soil,  why 
do  a  few  pounds  of  fertilizer  increase  the  supply  available  to  plants  ? 

3.  Where  are  most  of  the  potash  fertilizers  obtained? 

4.  Name  the  potash  fertilizers. 

5.  Describe  the  effects  of  potash  on  plant  growth. 

6.  Name  some  crops  that  are  particularly  benefited  by  potash. 

7.  Is  there  any  indication  that  the  use  of  sulfur  as  a  fertilizer 
may  be  desirable  ? 

8.  In  what  manures  and  fertilizers  is  sulfur  contained  ? 

LABORATORY   EXERCISES 

Exercise  I.  —  In  Exercise  V,  Chapter  I,  an  experiment  designed 
to  show  the  importance  of  three  plant-food  materials  to  plant 
growth  was  described.  If  this  test  has  been  properly  carried  out  it 
should  now  be  available  to  show  the  effects  of  potash  on  plant  de- 
velopment. 

Exercise  II.  —  Examination  and  identification  of  potash  fer- 
tilizers and  sulfur. 

Materials.  —  Set  of  fertilizers  (consisting  of  muriate  of  potash, 
sulfate  of  potash,  wood  ashes  and  sulfur),  nitric  acid,  hydrochloric 
acid,  silver  nitrate,  filter  paper  and  funnel,  flame,  litmus  paper. 

Procedure.  —  The  fertilizers  should  be  studied  and  tested  until 
identification  is  sure. 

Muriate  of  Potash 

This  salt  is  placed  on  the  market  as  opaque  crystals,  soluble  in 
water. 

Dissolve  a  small  portion  of  the  fertilizer  in  water  and  filter. 
Add  a  drop  of  nitric  acid  and  then  silver  nitrate.  A  white  curdy 
precipitate  indicates  the  presence  of  muriate. 


186  SOILS   AND   FERTILIZERS 

Sulfate  of  Potash 

This  salt  appears  as  a  light  yellowish  powder,  soluble  in  water  and 
non-deliquescent. 

Dip  a  crystal  in  hydrochloric  acid  and  then  place  in  the  flame. 
The  violet  color  is  a  test  for  potash. 

Wood  Ashes 

Wood  ashes  are  so  characteristic  as  to  need  but  little  description. 
Leach  a  small  portion  with  water  and  test  the  percolate  with  litmus 
paper. 

Sulfur 

Sulfur  is  a  yellowish  gray  powder.  It  melts  readily  and  burns 
with  a  bluish  flame,  giving  a  characteristic  odor.  It  is  insoluble  in 
water. 

Exercise  III.  —  Comparison  of  fertilizer  effects  on  plant 
growth. 

Materials.  —  Fertilizers,  flower  pots,  poor  sandy  soil,  oat  seed. 

Procedure.  —  The  study  of  the  effect  of  the  various  potash  fer- 
tilizers as  well  as  of  sulfur  might  be  of  value.  Fill  the  required 
number  of  flower  pots  with  the  same  quantity  of  a  poor  sandy  loam 
after  thoroughly  mixing  the  fertilizer  with  the  soil. 

If  the  effects  of  the  various  potash  fertilizers  are  to  be  compared 
add  them  respectively  at  the  rate  of  250  pounds  per  acre  (1  of  fer- 
tilizer to  10,000  of  soil).  Apply  at  same  time  sodium  nitrate  and 
acid  phosphate  at  the  rate  of  1  of  fertilizer  to  5000  of  soil  respec- 
tively. Add  one  gram  of  lime  to  each  pot.  Leave  one  pot  un- 
treated with  potash  fertilizers  as  a  check. 

If  sulfur  is  to  be  used  apply  it  at  the  rate  of  250  pounds  per  acre. 
Leave  one  pot  with  no  treatment,  have  one  to  which  only  sulfur  is 
applied,  prepare  a  third  with  a  complete  fertilizer  only  (mixture 
of  equal  parts  of  sodium  nitrate,  acid  phosphate  and  sulfate  of 
potash  applied  at  the  rate  of  1  of  fertilizer  mixture  to  5000  of  soil), 
and  a  fourth  pot  with  sulfur  plus  the  complete  fertilizer. 

Carry  out  the  experiment  as  explained  in  Exercise  III,  Chapter 
XI,  and  observe  results. 


CHAPTER  XIV 
LIME 

In  the  chapter  on  acid  soils,  reference  was  made  to  lime 
as  a  corrective  of  acidity.  Lime  is  not  a  fertilizer  in  the 
same  sense  as  are  the  substances  that  have  been  discussed 
in  the  last  three  chapters.  It  is,  to  be  sure,  an  indispensable 
ingredient  of  plant  tissue,  but  as  it  is  generally  present  in 
sufficient  quantity  in  arable  soils,  and  as  it  is  rather  soluble, 
there  is  usually  enough  lime  to  fully  supply  plant  growth,  and 
this  in  spite  of  the  fact  that  the  soil  may  be  greatly  in  need 
of  liming.  It  is  because  of  its  effect  on  the  soil,  rather  than 
directly  on  the  plant,  that  lime  is  used  as  a  soil  amendment. 

241.  Forms  of  lime.  —  The  forms  in  which  lime  is  used 
on  soils  are  (1)  ground  limestone,  (2)  marl,  (3)  air-slaked 
lime,  (4)  quick-lime  and  (5)  water-slaked  lime.  The  first 
three  of  these  are  similar  in  their  effects,  and  are  chemically 
alike,  being  what  is  termed  carbonate  of  lime.  Quick-lime 
and  water-slaked  lime  have  much  the  same  action  on  soils, 
and  are  called  caustic  lime. 

Quick-lime  is  made  by  burning  limestone  in  a  kiln.  Quick- 
lime, when  treated  with  water,  forms  water-slaked  lime. 
Air-slaked  lime  is  quick-lime  that  has  been  exposed  to  dry 
air  until  it  has  lost  its  caustic  properties.  Marl  is  found  in 
beds  in  the  earth,  as  is  limestone,  but  it  is  softer  than  lime- 
stone.    Like  limestone  it  is  ground  before  being  used. 

Owing  to  the  combinations  of  the  lime  itself  with  water 
and  gases  in  these  various  forms,  there  is  required  a  greater 
weight  of  some  forms  than  of  others  to  give  the  same  quantity 

187 


188  SOILS   AND   FERTILIZERS 

of  lime.  When  the  materials  are  fairly, pure,  the  number  of 
pounds  of  each  required  to  give  approximately  equivalent 
quantities  of  lime  are  as  follows : 

Quick-lime 56  pounds 

Water-slaked  lime  .     . . 74  pounds 

Air-slaked  lime,  marl,  ground  limestone  .     100  pounds 

When  applying  lime  to  land,  these  relationships  should  be 
kept  in  mind.  If  it  is  a  question  of  using  quick-lime  or  ground 
limestone  one  must  provide  nearly  twice  as  much  limestone 
as  quick-lime  in  order  to  apply  an  equal  quantity  of  lime. 

242.  Absorption  of  lime  by  soils.  —  In  the  forms  in  which 
it  is  applied  to  soils,  lime  is  not  so  soluble  as  potash  fertilizers. 
When  brought  in  contact  with  soil,  the  lime  is  absorbed  and 
rendered  still  less  soluble.  It  is,  however,  somewhat  more 
soluble  than  soil  potash,  and  drainage  waters  usually  con- 
tain several  times  as  much  lime  as  potash.  It  is  the  soluble 
part  of  the  lime  that  has  the  beneficial  effect  on  crops  and 
soils.  The  ways  in  which  the  benefit  accrues  are  numerous 
and  will  be  described  in  a  number  of  the  following  para- 
graphs. Lime  is  usually  applied  in  much  greater  quantities 
than  are  fertilizers,  but  the  treatment  is  given  only  at  inter- 
vals of  four  or  five  years. 

243.  Lime  requirement  of  soils.  —  It  is  possible,  by  means 
of  chemical  methods,  to  ascertain  how  much  lime  a  soil  will 
absorb  before  it  shows  alkalinity  due  to  the  presence  of  an 
excess.  Such  a  test  is  useful  to  indicate  the  quantity  of  lime 
that  should  be  applied  to  a  soil  in  order  that  it  shall  be  at 
least  temporarily  adapted  to  the  production  of  lime-loving 
plants. 

The  results  of  such  a  test  are  usually  expressed  in  pounds 
of  lime  required  to  satisfy  the  absorptive  properties  of  a 
certain  number  of  pounds  of  soil,  as  for  instance,  2,000,000 
pounds.  This  will  vary  in  different  soils  from  none  to  several 
thousand  pounds. 


LIME 


189 


244.  Effect  of  lime  on  tilth.  —  A  clay  or  loam  soil  when  in 
acid  condition  tends  to  become  compact  and  difficult  to  till. 
The  addition  of  lime  to  soil  helps  to  bring  about  a  granular 
formation  of  the  small  particles,  and  to  give  the  soil  better 
tilth.     This  effect  has  previously  been  noted  in  §  46. 

245.  Effect  of  lime  on  bacterial  action.  —  Some  of  the 
most  beneficial  bacteriological  processes  are  greatly  favored 
by  an  abundant  supply  of  lime  in  the  soil.  Important  among 
these  are  the  various  processes  involved  in  the  formation 
of  nitrates  from  organic  forms  of  nitrogen.  It  seems  also 
to  be  associated  with  the  operation  by  which  some  legumes, 
for  instance  alfalfa,  secure  nitrogen  from  the  air.  The  in- 
creased supply  of  easily  available  nitrogen  is  often  reflected 
in  the  yield  and  nitrogen  content  of  the  crops,  as  well  as  in 
the  percentage  of  nitrates  in  the  soil.  This  is  illustrated  by 
an  experiment  in  which  alfalfa  was  raised  on  plats  of  land 
one  of  which  was  limed  liberally  and  the  other  not  limed. 
The  hay  was  weighed  when  cut,  and  was  then  analyzed, 
as  were  also  the  weeds  growing  with  the  alfalfa.  The  soil 
was  sampled  and  the  nitrates  determined.  The  soil  was  also 
allowed  to  stand  for  ten  days  at  an  optimum  water  content 
and  a  temperature  suited  to  the  production  of  nitrates, 
at  the  end  of  which  time  the  quantities  of  nitrates  formed 
were  determined.     The  results  are  shown  in  Table  40. 


Table  40.  —  The  Effect  of  Liming  Soil  on  the  Yield  and 
Composition  of  Alfalfa  Raised  on  It,  and  on  Its  Nitri- 
fying Power 


» 

Limed 

Not  Limed 

Yield  of  hay,  pounds  on  plat      .     .     .     . 

103 

75 

Percentage  of  protein  in  alfalfa  .... 

20.63 

15.88 

Percentage  of  protein  in  weeds  .... 

10.67 

8.79 

Nitrates  in  dry  soil,  parts  per  million 

8.10 

4.30 

Nitrates  produced  in  ten  days,     "       . 

176.00 

92.00 

190  SOILS   AND   FERTILIZERS 

The  effect  of  the  lime  was  not  only  to  increase  the  yield  of 
alfalfa  hay,  but  also  its  protein  content,  as  well  as  that  of  the 
weeds  growing  with  it.  The  rate  of  nitrate  formation  in  the 
soil  was  also  greater  when  limed. 

246.  Liberation  of  plant-food  materials.  —  It  has  gen- 
erally been  held  that  the  application  of  lime  to  soils  renders 
some  of  the  other  plant  nutrients  more  soluble  by  reason 
of  the  exchange  of  lime  for  these  substances  in  the  insoluble 
combinations  found  in  soils.  This  has  been  discussed  in 
section  115.  There  is  little  doubt  that  magnesia  is  thus 
rendered  more  available,  but  magnesia  is  rarely  lacking. 
Potash  is  often  said  to  be  made  soluble,  but  although  such  may 
be  the  case  with  some  soils  it  is  probably  not  true  of  all,  and 
there  is  really  little  evidence  to  substantiate  the  claim  in  any 
case.  The  use  of  lime,  under  some  soil  conditions,  may  render 
phosphoric  acid  more  available,  probably  by  supplying  a  base 
more  soluble  than  iron  or  alumina,  with  which,  in  soils  defi- 
cient in  lime,  the  phosphoric  acid  might  otherwise  be  combined. 

247.  Effect  on  plant  diseases.  —  The  presence  of  abun- 
dance of  lime  retards  the  development  of  certain  plant  diseases, 
such  as  the  "  finger-and-toe  "  disease  to  which  cabbages 
and  some  root  crops  are  subject.  On  the  other  hand,  it 
may  promote  some  diseases,  as,  for  example,  potato  scab. 

248.  The  use  of  inagnesian  limes.  —  Some  limestone 
contains  a  considerable  proportion  of  magnesia.  When 
grown  in  water  cultures,  many  agricultural  plants  are  injured 
when  the  proportion  of  magnesia  is  greater  than  that  of 
lime.  In  soil,  however,  magnesia  is  not  nearly  as  soluble 
as  lime  and  consequently  there  may  be  many  times  more 
magnesia  than  lime  present  without  as  much  actually  being 
in  solution.  Hence  it  is  seldom  that  magnesia  is  injurious, 
and  magnesian  lime  may  be  used  to  overcome  soil  acidity 
except  possibly  in  the  few  soils  in  which  the  ratio  of  magnesia 
to  lime  is  already  very  high. 


LIME 


191 


249.  Caustic  lime  versus  ground  limestone.  —  As  lime 
helps  to  correct  soil  acidity  no  matter  in  what  form  it  is 
applied,  there  is  little  advantage  in  one  form  over  another 
so  long  as  it  is  remembered. that  100  pounds  of  ground  lime- 
stone are  equivalent  to  56  pounds  of  freshly  burnt  lime,  and 
provided  the  cost,  hauling  included,  is  in  that  ratio.  The 
greater  ease  with  which  ground  limestone  may  be  handled 
would,  under  these  circumstances,  give  it  the  preference. 

In  respect  to  its  effect  on  tilth,  lime,  in  the  caustic  form, 
is  apparently  more  effective  than  when  in  the  form  of  ground 
limestone.  For  heavy  clay  soil,  the  compact  and  cloddy 
condition  of  which  presents  a  serious  difficulty,  caustic  lime 
is  preferable.  A  comparison  of  these  two  forms  of  lime  on  a 
heavy  clay  soil  is  shown  in  the  following  table  in  which  the 
average  percentage  increase  in  crops  from  the  limed  over  the 
unlimed  plats  for  a  period  of  five  years  is  stated. 

Table  41.  —  Average  Percentage  Increase  in  Yield  Due  to 
Caustic  Lime  and  Ground  Limestone 


Form  of  Limb  Applied 


Caustic  lime 

Ground  limestone     .     .     .     . 

Caustic  lime 

Ground  limestone  .  .  .  . 
Caustic  magnesian  lime  .  . 
Ground  magnesian  limestone 


Pounds 
Applied 
per  Acre 


3000 
6000 
1000 
2000 
2000 
3225 


Percentage 

Increase  in 

Yield  of 

Crops 


20.9 
14.8 
3.9 
3.7 
6.7 
3.3 


250.  Fineness  of  grinding  limestone.  —  The  greater 
solubility  of  finely  ground  material,  as  compared  with  coarse, 
makes  it  desirable  that  limestone  be  at  least  fairly  well 
pulverized  before  it  is  used.  If  it  is  so  ground  that  all  of  the 
particles  will  pass  through  a  sieve  having  50  meshes  to  the 


192     <  SOILS   AND   FERTILIZERS 

inch,  it  will  probably  be  just  as  effective  as  if  ground  much 
finer. 

251.  Gypsum  or  land  plaster.  —  In  the  early  agriculture 
of  this  country,  before  ordinary  commercial  fertilizers  were 
used,  gypsum  was  a  popular  soil  amendment.  Its  effective- 
ness has  apparently  decreased  as  the  soils  on  which  it  was 
used  have  been  longer  under  cultivation.  It  has  generally 
been  credited  with  liberating  potash,  and  possibly  as  the 
soils  have  become  more  acid  it  has  been  less  effective  in  this 
respect.     At  any  rate,  it  is  rarely  used  at  present. 

Gypsum  has  little  effect  on  tilth  and  is  not  in  any  sense 
a  substitute  for  caustic  lime  for  that  purpose,  nor  is  it  of 
any  value  to  overcome  soil  acidity,  as  it  contains  a  strong 
acid. 

QUESTIONS 

1.  How  does  the  need  of  a  soil  for  lime  differ,  in  principle,  from 
its  need  for  the  other  fertilizers  we  have  studied  ? 

2.  Name  the  forms  in  which  lime  is  applied  to  soils. 

3.  Which  of  these  are  similar  chemically  and  in  their  effect  on 
soils  ? 

4.  How  is  quick-lime  made  ?  Water-slaked  lime  ?  Air-slacked 
lime? 

5.  How  does  the  solubility  of  lime  compare  with  that  of  potash, 
when  both  are  absorbed  by  soil  ? 

6.  What  is  shown  by  a  chemical  determination  of  the  lime 
requirement  of  a  soil  ? 

7.  What  is  the  effect  of  lime  on  some  of  the  bacteriological  pro- 
cesses in  soil  ? 

8.  How  does  lime  affect  the  availability  of  certain  other  plant 
nutrients  in  soil  ? 

9.  What  is  its  effect  on  certain  plant  diseases  ? 

10.  Discuss  the  use  of  magnesian  limes. 

11.  Discuss  the  use  of  caustic  lime  as  compared  with  ground 
limestone. 

12.  How  does  the  fineness  of  grinding  limestone  affect  its  imme- 
diate usefulness  ? 

13.  How  does  gypsum  affect  soil  ? 


LIME  193 

LABORATORY   EXERCISES 

Exercise  I.  —  A  study  of  the  forms  of  lime. 

Materials.  —  Set  of  lime  samples  (ground  limestone,  marl,  quick- 
lime, hydrate  of  lime  and  gypsum),  hand  lens,  muriatic  acid,  litmus 
paper. 

Procedure.  —  Study  the  various  forms  of  lime  until  identifica- 
tion is  easy. 

Ground   Limestone  and  Marl 

Ground  limestone  can  be  detected  by  its  physical  condition,  es- 
pecially if  a  hand  lens  is  used.  It  is  practically  insoluble  in  water. 
Its  color  varies  from  white  to  gray.  The  presence  of  carbonates 
may  be  detected  by  a  few  drops  of  dilute  muriatic  acid. 

Marl  is  a  soft  powdery  form  of  calcium  carbonate.  Its  texture 
and  the  presence  of  shells  and  organic  matter  serve  to  distinguish 
it  from  ground  limestone. 

Quick-lime 

Quick-lime  appears  on  the  market  either  in  lumps  or  as  a  fine 
powder.  It  is  very  caustic  and  intensely  alkaline  to  litmus  paper. 
When  in  contact  with  water  it  heats  and  slakes,  becoming  hydrate 
of  lime.  This  characteristic  distinguishes  it  from  the  other  forms 
of  lime. 

Hydrate  of  Lime 

This  form  of  lime  is  a  white  powder,  soluble  in  water.  Its  sour 
taste  serves  to  distinguish  it  from  marl  and  limestone.  It  is  alka- 
line to  litmus  paper. 

Gypsum 

This  amendment  is  marketed  as  a  grayish  to  white  powder,  in- 
soluble in  water.  It  is  calcium  sulfate.  It  does  not  react  with  acid 
as  does  the  limestone  nor  with  water  as  does  the  lump  lime.  Its 
lack  of  taste  distinguishes  it  from  hydrate  of  lime. 

Exercise  II.  —  Fineness  of  ground  limestone. 

Materials.  —  Samples  of  limestone,  10,  20,  40,  60  and  100  mesh 
sieves,  balance  and  weights. 

Procedure.  —  The  fineness  of  ground  limestone  has  a  marked 
effect  on  its  value.  Weigh  out  100-gram  portions  of  the  various 
samples  of  limestone  and  pass  them  through  the  sieves.  Weigh 
o 


194  SOILS   AND   FERTILIZERS 

the  resulting  grades  and  calculate  the  proportion  of  the  original 
sample  passing  through  the  different  mesh  sieves.  Try  to  make  a 
relative  estimate  of  the  value  of  the  various  samples  on  this  basis. 

Exercise  III.  —  Effect  of  lime  on  biological  action. 

Materials.  —  An  acid  soil  from  under  sod,  two  8-ounce,  wide- 
mouth  bottles,  hydrate  of  lime,  large  vessel  for  mixing  soil  and 
water,  funnel  and  filter  paper,  evaporating  dishes,  water  bath, 
phenoldisulphonic  acid,  ammonia,  flame,  two  100  c.c.  graduated 
cylinders. 

Procedure.  —  Place  50-gram  samples  of  the  acid  soil  in  each  of 
two  8-ounce  bottles.  Add  and  mix  well  with  one  gram  of  carbonate 
of  lime.  Bring  the  soils  in  each  bottle  up  to  optimum  moisture 
content.  Plug  mouths  lightly  with  cotton  and  set  aside  at  opti- 
mum temperature  for  a  week. 

Now  estimate  nitrates  in  manner  described  in  Exercise  I,  Chap- 
ter IX.  A  comparison  of  the  results  will  show  the  influence  of  lime 
on  nitrification.     Apply  these  results  to  practical  problems. 

Exercise  IV.  —  Flocculation  by  lime. 

Materials.  —  Ground  limestones  and  hydrate  of  lime  ;  large 
bottle  for  preparing  soil  suspension,  two  100  c.c.  graduated  cylinders. 

Procedure.  —  Prepare  a  soil  suspension  by  shaking  a  heavy 
clay  soil  for  15  minutes  in  a  bottle  partially  filled  with  water  (one 
of  soil  to  ten  of  water)  after  adding  a  few  drops  of  strong  ammonia. 
Allow  to  stand  for  two  or  three  hours  and  then  pour  suspension  into 
the  cylinders.  Fill  to  100  mark.  Now  add  to  one  a  pinch  of  hy- 
drate of  lime  and  to  the  other  the  same  amount  of  ground  lime- 
stone.    Shake  well  and  allow  to  stand. 

Watch  closely  and  explain  results.  Apply  the  principle  involved 
here  to  actual  field  practice. 

Exercise  V.  —  Flocculation  by  lime. 

Materials.  —  Clay  soil  and  hydrate  of  lime. 

Procedure.  —  Prepare  from  one  portion  of  clay  soil  a  well-puddled 
ball.  Add  hydrate  of  lime  to  another  portion  of  the  clay  soil  (rate, 
1  of  lime  to  500  of  soil),  and  work  into  a  ball  after  adding  sufficient 
water.  Allow  the  two  samples  to  dry  thoroughly.  Crush  each  one. 
Note  difference  in  crushing  resistance  and  the  structural  character 
of  each  soil.     Apply  results  to  actual  field  practice. 

Exercise  VI.  —  Lime  and  the  rotation. 

The  place  of  lime  in  a  rotation  depends  on  a  number  of  factors. 
Discuss  these  with  the  student.     Take  a  number  of  standard  rota- 


LIME  195 

tions  and  decide  where  in  the  rotation  the  lime  should  come  and 
why. 

Encourage  the  pupils  to  obtain  the  rotations  used  on  their  home 
farms  and  discuss  lime  in  relation  to  such  rotations.  It  might  also 
be  well  to  visit  some  good  farmer  and  discuss  with  him  the  form  of 
lime  he  buys,  how  he  applies  it,  what  amounts  he  uses  and  where  in 
the  rotation  he  adds  it  to  the  soil.  The  practical  phases  of  the  use 
of  lime  are  what  the  pupil  should  understand. 

Exercise  VII.  —  Problems  —  Forms  of  lime  to  apply. 

In  buying  lime  the  form  that  will  give  the  greatest  amount  of 
calcium  for  the  money  is  usually  purchased  unless  the  flocculating 
effect  of  burnt  lime  is  necessary.  The  relative  value  of  the  lime,  the 
cost  per  ton,  the  freight  and  the  cost  of  application  must  be  con- 
sidered. For  a  rough  calculation  50  pounds  of  burnt  lime  is  con- 
sidered equal  to  75  pounds  of  hydrate  and  to  100  pounds  of  ground 
limestone. 

Problem  1.  —  A  farmer  located  on  land  already  sufficiently  fri- 
able, wishes  to  apply  one  ton  of  burnt  lime  or  its  equivalent  in  other 
forms.  Burnt  lime  costs  him  $5.00  per  ton  f.  o.  b.,  hydrate  lime 
$4.00  and  ground  limestone  $2.25  per  ton.  Freight  is  25^  per  ton, 
as  is  also  hauling  and  application  together.  Which  form  of  lime 
should  the  farmer  buy  ? 

Problem  2.  —  The  next  year  the  f.  o.  b.  price  of  lime  changed  to 
$4.90,  $3.00  and  $2.00  for  the  burnt  lime,  the  hydrate  and  the 
limestone,  respectively.  Considering  freight  and  cost  of  haul  and 
application  the  same  as  before,  what  form  should  be  purchased  ? 

Problem  3.  —  This  same  farmer  can  purchase  marl  at  $1.00  per 
ton,  but  he  must  load  it  himself  and  haul  it  three  miles  over  a  dirt 
road.  It  is  impure,  carrying  only  two-thirds  the  calcium  that  the 
limestone  has.  From  conditions  in  your  locality  how  would  you 
consider  the  desirability  of  purchasing  this  form  of  lime  as  com- 
pared with  those  forms  mentioned  in  Problem  2  ? 


CHAPTER  XV 
THE  PURCHASE  AND  MIXING  OF  FERTILIZERS 

It  is  hardly  three-quarters  of  a  century  since  the  fertilizer 
industry  began  its  development.  In  that  time  the  use  of 
commercial  fertilizers  has  spread  to  all  the  important  agri- 
cultural states  of  this  country.  Their  sale  amounts  to 
more  than  $110,000,000  annually,  of  which  fully  one-half 
is  expended  by  the  farmers  of  the  South  Atlantic  states, 
in  an  area  lying  within  three  hundred  miles  of  the  seaboard. 
Nearly  one-half  of  the  remainder  is  purchased  in  the  Middle 
Atlantic  and  New  England  states,  while  only  about  five 
percent  is  used  west  of  the  Mississippi  river. 
J  A  large  utilization  of  fertilizers  in  a  region  is  often,  but 
not  always,  an  indication  of  an  intensive  agriculture.  The 
importance  of  fertilizers  in  farm  practice  and  the  large 
expenditure  that  their  use  involves,  together  with  the  possi- 
bilities for  profit,  when  they  are  properly  used,  make  it  de- 
sirable that  those  who  utilize  fertilizers  should  thoroughly 
understand  the  commercial,  as  well  as  the  agricultural, 
values  of  these  products. 

252.  Brands  of  fertilizers.  —  The  various  fertilizer  con- 
stituents or  carriers  that  have  been  described  are  purchased 
toy  fertilizer  manufacturers,  who  mix  them  into  various 
combinations,  each  of  which  is  called  a  brand.  Each  of 
these  brands  usually  contains  nitrogen,  phosphoric  acid 
and   potash,  in   which  case  it  is  called  a  complete  ferti- 

196 


THE   PURCHASE   AND   MIXING  OF   FERTILIZERS     197 


198  SOILS   AND   FERTILIZERS 

lizer,  although  occasionally  a  brand  of  fertilizer  will  have 
only  two  carriers.  Each  brand  is  given  a  trade  name,  fre- 
quently implying  the  usefulness  of  the  fertilizer  for  some 
particular  crop,  but  without  reference  to  the  character 
of  the  soil  on  which  it  is  to  be  used.  It  is  better,  how- 
ever, to  purchase  a  fertilizer  on  the  basis  of  its  composi- 
tion rather  than  because  of  its  name.  The  composition 
of  fertilizers  for  different  crops  will  be  discussed  later  (see 
§  261). 

If,  in  compounding  a  fertilizer,  those  carriers  are  used 
that  are  difficultly  soluble,  the  fertilizer  is  not  so  valuable 
as  if  composed  of  easily  soluble  substances.  The  solubility 
as  well  as  the  percentage  of  each  ingredient  should  be  known 
to  the  purchaser. 

253.  High-grade  and  low-grade  fertilizers.  —  A  fertilizer  is 
known  on  the  market  as  high-grade  or  low-grade,  depending 
on  the  percentage  of  fertilizing  constituents  that  it  contains, 
or  on  the  availability  of  its  plant-food  materials.  Low-grade 
fertilizers  cost  less  than  high-grade  because  thej'  contain 
less  plant-food  material  or  because  they  are  less  soluble, 
although  the  price  of  a  pound  of  the  plant  nutrients  may  be  no 
less,  and,  in  fact,  is  usually  more.  The  low-grade  product 
is  encumbered  with  a  large  amount  of  inert  material,  that 
adds  to  the  cost  of  transportation  and  handling,  without 
adding  to  the  value  of  the  fertilizer.  For  these  reasons  the 
cost  of  a  pound  of  any  one  of  the  plant  nutrients  is  usually 
less  in  high-grade  than  in  low-grade  goods.  A  ton  of  low- 
grade  fertilizer  may  contain  500  or  600  pounds  more  inert 
material  than  a  high-grade  fertilizer,  upon  which  freight 
must  be  paid,  and  which  must  be  hauled  from  the  station 
and  spread  on  the  field. 

The  following  figures  were  obtained  by  tabulating  one 
hundred  and  thirty  brands  of  fertilizers  analyzed  at  the 
Vermont  Experiment  Station. 


THE   PURCHASE   AND   MIXING  OF   FERTILIZERS     199 

Table  42.  —  Comparative  Values  of  Low-Grade,  Medium  and 
High-Grade  Fertilizers 


M 

8« 

Cost  in  Cents  of 

M 

a 

Sg 

One  Pound  of 

N    % 

a 

M 
«  2 

9 

§5 

<*>3 

bM  O 

dw8 

Fertilizer 

'S 

< 

22 

S  3 

ft  J 

£  j  a 
3«  s 

6^ 

1  , 

2  d 

8T  OF   P 
)RTH   OF 

Hands 

RMER 

2 

'E 
o 

01 

c3 

a  ^a 
o  g« 

Sod 

o  < 

So«i 

*  3 

°£  4  < 

^ 

^  *5 

<J> 

MHfr 

Wo 

o£S£ 

£ 

PM 

dH 

>SQ 

High  grade    . 

$26.30 

#38.93 

$12.63 

$0.48 

28 

5.7 

6.3 

67.6 

Medium  grade 

18.22 

30.00 

11.78 

0.65 

31 

6.3 

7.0 

60.6 

Low  grade 

13.52 

27.10 

13.58 

1.00 

38 

7.6 

8.5 

50.0 

In  mixing  fertilizers  in  a  factory,  it  is  customary  to  incor- 
porate with  the  carriers  of  plant  nutrients  more  or  less  material 
that  has  no  influence  on  plant  growth,  but  that  serves  to  di- 
lute the  mixture  and  to  prevent  it  from  becoming  damp  by 
the  absorption  of  moisture,  and  also  to  prevent  the  chemical 
interaction  of  the  constituents.     This  material  is  called  a  filler. 

254.  Fertilizer  inspection  and  control.  —  Most  of  the 
states  have  enacted  legislation  providing  for  the  inspection 
and  control  of  the  sale  of  commercial  fertilizers.  Each 
brand  of  fertilizer,  that  sells  for  $5.00  or  more  a  ton,  must 
pay  a  state  license  fee  and  each  bag  must  bear  a  tag  stating 
the  guaranteed  percentage  of  nitrogen,  phosphoric  acid  and 
potash  that  the  fertilizer  contains,  and  giving  some  informa- 
tion in  regard  to  their  solubility. 

There  is  little  uniformity  in  the  requirements  of  the  dif- 
ferent states.  In  some  states  a  very  detailed  statement  of 
the  composition  of  the  fertilizer  and  the  solubility  of  its 
constituents  is  required.  The  following  information  is 
called  for  by  some  of  the  states. 

Percentage  of  nitrogen  in  the  following  forms : 


200  SOILS   AND   FERTILIZERS 

In  nitrates  and  ammonium  salts.  These  are  generally 
present  in  nitrate  of  soda  and  sulfate  of  ammonia.  Their 
availability  has  already  been  discussed  (see  §  218). 

Water-soluble  organic  nitrogen.  This  is  probably  not 
so  readily  available  as  the  two  former  kinds,  but  differs  little 
from  them  in  this  respect. 

Active  water-insoluble  organic  nitrogen.  Although  not 
directly  available  this  becomes  so  quickly  enough  for  the 
crop  to  which  it  is  applied  to  obtain  part  of  it. 

Inactive  water-insoluble  organic  nitrogen  is  that  part  of 
the  organic  nitrogen  that  is  of  little  value  for  immediate 
plant  growth. 

Percentage  of  phosphoric  acid  in  the  following  forms : 

Water-soluble  phosphoric  acid,  which  is  readily  available 
(see  §  227). 

Reverted  phosphoric  acid.  Not  so  readily  available 
(see  §  227). 

Available  phosphoric  acid.  This  usually  consists  of  the 
sum  of  the  two  forms  mentioned  above.  Sometimes  when 
this  term  is  used  no  distinction  is  made  between  the  water- 
soluble  and  the  reverted,  but  this  is  not  so  satisfactory. 

Insoluble  phosphoric  acid.  This  is  slowly  available,  but 
in  animal  products,  such  as  bone,  tankage  and  other  slaughter 
house  waste,  it  becomes  available  more  quickly  than  if  present 
in  rock  phosphate.  However,  the  analysis  does  not  distin- 
guish between  the  organic  and  inorganic  carriers. 

Percentage  of  potash  in  the  following  forms : 

Soluble  in  water. 

Present  as  chloride. 

255.  Trade  values  of  fertilizer  ingredients.  —  In  the 
states  having  fertilizer  inspection  laws,  it  is  customary  for 
the  officers  in  charge  of  the  inspection  to  adopt  each  year  a 
schedule  of  trade  values  for  nitrogen,  phosphoric  acid  and 
potash  in  each  of  the  carriers  ordinarily  found  in  fertilizers. 


THE  PURCHASE  AND  MIXING  OF  FERTILIZERS     201 

These  vrlues  are  based  on  the  whulesale  market  reports 
for  six  months  preceding  March  1  of  each  year,  to  which  is 
added  about  20  percent  of  the  price,  to  cover  cost  of  handling. 


Potato  Manure  "A"  without  Potash  1916 


Nitrogen  -  *  A  •  4.1 1    to    4.94  per  cent. 

Equal  to  Ammonia  ^^k  5.        to    6.  " 

Soluble  Phosphoric  Acid  ^^A  4.         to     5. 

Reverted  Phosphoric  Acid  ^^^^L  4.        to     S. 

Available  Phosphoric  Acid  -     M  ^^L  8.        to   10. 

Insoluble  Phosphoric  Acid  -  MgJ^^L  1.        to      2. 

Total  Phosphoric  Acid  '^^^^^^L  9'       to    ,2, 
MANUFACTURED  BY 

>C  -   Y-  Z  -  FERTILIZER  COMPANY 


Fig.  30. —Tag  representative  of  the  kind  often  used  on  bags  of  fertilizer 
to  state  the  percentages  of  their  constituents. 

The  following  values  are  for  the  year  1914. 
Trade  Values  of  Plant  Nutrients  in  Raw  Materials 

Value  per 
Pound 

in  Cents 

Nitrogen  in  nitrates 18.5 

Nitrogen  in  ammonium  salts 18.5 

Organic  nitrogen  in  dried  and  finely  ground  fish,  meat  and 

blood '.     .  20.0 

Organic  nitrogen  in  finely  ground  bone  and  tankage    .     .  19.0 

Organic  nitrogen  in  coarse  bone  and  tankage       ....  15.0 

Organic  nitrogen  in  castor  pomace  and  cottonseed  meal    .  20.0 

Phosphoric  acid,  water  soluble 4.5 

Phosphoric  acid,  reverted 4.0 

Phosphoric  acid  in  fine  bone,  fish  and  tankage  ....  4.C 
Phosphoric  acid  in  cottonseed  meal  and  castor  pomace  .  4.0 
Phosphoric  acid  in  coarse  fish,  bone,  tankage  and  ashes  .  3.5 
Phosphoric  acid  in  mixed  fertilizers,  insoluble  ....  2.0 
Potash  as  high-grade  sulfate,  in  forms  free  from  muriate, 

in  ashes,  etc 5.25 

Potash  as  muriate 4.25 

Potash  as  castor  pomace  and  cottonseed  meal    ....       5.0 


202  SOILS   AND   FERTILIZERS 

These  values  may  be  used  by  the  consumer  to  calculate 
the  wholesale  cost  of  a  fertilizer  of  guaranteed  composition, 
which  he  can  then  compare  with  the  retail  price  asked  by 
the  retail  dealer.  He  may  also  compare  the  relative  values 
of  brands  of  similar  composition  offered  for  sale  by  different 
manufacturers. 

256.  Computation  of  the  wholesale  value  of  a  fertilizer.  — 
Suppose  that  we  have  the  following  statement  of  the  analysis 
of  a  fertilizer. 

Per  Cent 

Nitrogen  in  nitrate  of  soda 1 

Nitrogen  in  dried  blood        2 

Phosphoric  acid,  water  soluble 6 

Phosphoric  acid,  reverted 2 

Potash,  as  muriate 10 

The  number  of  pounds  of  each  constituent  to  a  ton  of 
fertilizer  is  then  found  by  multiplying  the  weight  of  a  ton 
of  fertilizer  by  the  percentage  of  the  constituent,  thus  : 

Nitrogen,  as  nitrate  .01  X  2000  =  20  pounds  per  ton. 

Nitrogen  in  dried  blood  .02  x  2000  =  40  pounds  per  ton. 

Phosphoric  acid,  water-soluble  .06  X  2000  =  120  pounds  per  ton. 
Phosphoric  acid,  reverted  .02  X  2000  =  40  pounds  per  ton. 

Potash,  muriate  .10  X  2000  =  200  pounds  per  ton. 

The  trade  values,  as  published  by  the  fertilizer  inspection 
officers,  are  then  applied  to  the  several  constituents. 

Nitrogen  as  nitrate  20  X  $.185   =  $  3.70 

Nitrogen  in  dried  blood  40  x  $.20     =      8.00 

Phosphoric  acid,  water-soluble    120  X  $.045   =      5.40 
Phosphoric  acid,  reverted  40  x  $.04      =      1.60 

Potash,  muriate  200  X  $.0425  =      8.50 

$27.20 

Such  a  fertilizer  will  cost  the  consumer  more  than  the  fig- 
ure derived  in  this  way,  because  the  entire  cost  of  mixing 
and  retailing  must  be  added  to  it.  It  may  serve  as  a  basis 
for  ascertaining  whether  it  would  not  be  more  profitable 


THE   PURCHASE   AND   MIXING  OF   FERTILIZERS     203 

for  a  group  of  consumers  to  purchase  the  fertilizer  ingredients 
in  car-load  lots  and  do  the  mixing  themselves. 

It  must  also  be  remembered  that  this  is  the  commercial 
value  and  not  necessarily  the  agricultural  value,  which  latter 
is  determined  by  the  profits  from  its  use,  and  will  depend  on 
many  factors. 

.  257.  Home  mixing  of  fertilizers.  —  There  is  a  large  margin 
between  the  trade  value  of  fertilizer  ingredients  and  their 
retail  price  as  sold  by  the  dealer.  The  cost  of  the  raw  ma- 
terials often  doubles  in  the  process  of  mixing  and  retailing, 
with  the  necessary  transportation.  It  has  been  demon- 
strated that  the  raw  materials  may  be  purchased  from  the 
wholesale  dealer  and  mixed  by  the  consumer  at  a  consider- 
ably lower  cost  than  if  purchased  mixed  from  the  retail  dealer, 
and  that  the  results  are  fully  as  satisfactory. 

Other  advantages  from  home  mixing  are  that  it  permits 
the  farmer  to  use  exactly  the  proportion  of  the  several  con- 
stituents that  he  desires,  and  that  it  makes  unnecessary 
the  handling  of  a  large  amount  of  inert  materials  frequently 
contained  in  mixed  fertilizers.  It  is  thus  possible  for  him 
to  ascertain,  by  field  tests,  the  best  proportions  of  the  various 
fertilizer  constituents  to  use  on  his  own  land  for  each  of  the 
crops  he  is  growing.  This  knowledge  makes  it  possible  to 
decrease  greatly  the  expenditure  for  fertilizers. 

258.  Fertilizers  that  should  not  be  mixed.  —  Because 
fertilizers  consist  of  chemicals,  some  of  which  react  on  each 
other  to  form  compounds  different  from  those  in  the  original 
substances,  it  is  unwise  to  mix  certain  of  these  carriers. 
The  result  may  be  to  convert  soluble  nutrients  into  insoluble 
ones,  or  to  cause  the  loss  of  some  constituent  in  the  form 
of  gas.  If  one  is  to  mix  his  own  fertilizers  he  must  know 
what  materials  should  not  be  brought  in  contact.  The  fol- 
lowing are  some  of  the  common  carriers  that  should  not 
be  mixed : 


204  SOILS   AND   FERTILIZERS 

Caustic  lime  1  f.    .,    ,       ,  .■  ■■ 

iT7     j      i_  .lL    Acid  phosphate 

Wood  ashes  >  with  <  ^.      f     .  \ 
-„     .     ,  Dissolved  bone 

Basic  slag 

Cyanamid 
Caustic  lime 
Wood  ashes 
Basic  slag 


with 


'  Sulfate  of  ammonia 
Slaughter  house   waste   containing  ni- 

trogen 
Farm  manure 


The  following  mixtures  should  be  applied  immediately : 

)f  Nitrate  of  soda 
with  <  Muriate  of  potash 
[  Kainit 
Acid  phosphate    with    Nitrate  of  soda  or  ground  limestone. 

Cyanamid  should  not  be  mixed  with  acid  phosphate  if 
there  is  more  than  one  part  of  the  former  to  ten  of  the  latter. 

259.  Calculation  of  a  fertilizer  mixture.  —  In  deciding 
on  the  composition  of  fertilizers  the  best  and  simplest  way 
is  to  consider  them  according  to  the  percentage  of  each  of 
the  three  constituents,  nitrogen,  phosphoric  acid  and  potash, 
they  contain,  /if  we  decide  to  use  a  3-8-5  fertilizer,  the 
next  step  is  to  calculate  how  many  pounds  of  each  of  the 
carriers  of  these  substances  must  be  used  for  each  ton  of  the 
complete  fertilizer,  and  how  much  filler  must  be  added. 
Suppose  we  have  on  hand  the  following  carriers : 

Nitrate  of  soda  containing  15  percent  nitrogen 

Acid  phosphate  containing  14  percent  available  phosphoric  acid 

Muriate  of  potash,  containing  50  percent  potash 

>  The  first  step  is  to  calculate  the  number  of  pounds  of 
nitrogen,  of  phosphoric  acid  and  of  potash  in  a  ton  of  a 
3-8-5  fertilizer.  To  do  this  we  merely  multiply  the  num- 
ber of  pounds  in  a  ton  by  the  percent  of  each  plant-food 
material. 


THE  PURCHASE   AND   MIXING  OF  FERTILIZERS     205 

2000  x  .03  =    60  pounds  nitrogen  per  ton 

2000  X  .08  =  160  pounds  phosphoric  acid  per  ton 

2000  X  .05  =  100  pounds  potash  per  ton 

The  next  step  is  to  calculate  the  number  of  pounds  of  the 
carrier  required  to  furnish  the  quantity  of  plant-food  material 
that  has  just  been  found.  This  is  done  by  dividing  the 
weight  of  the  plant-food  material  required  by  the  percent 
of  this  particular  plant-food  material  in  the  carrier  that  is 
to  be  used. 

60  •*-  .15  =    400  pounds  nitrate  soda 
160  ■¥■  .14  =  1143  pounds  acid  phosphate 
100  +  .50  =    200  pounds  muriate  of  potash 
1743  pounds  of  the  three  carriers 

The  weights  of  the  different  carriers  are  then  added,  giving 
in  this  case  1743  pounds  needed  for  every  ton  of  fertilizer. 
The  remainder  of  the  ton  (2000  -  1743  =  257  pounds) 
is  then  made  up  with  a  filler,  consisting  of  sand,  dry  earth, 
muck,  peat,  sawdust  or  something  of  the  kind. 

260.  How  to  mix  the  ingredients.  —  A  smooth  tight  floor 
is  needed  on  which  each  carrier  is  spread  in  turn  to  break 
down  the  lumps.  It  is  then  passed  through  a  coarse  screen. 
A  weighed  quantity  of  the  filler  or  principal  carrier  is  then 
spread  out  in  uniform  depth  and  on  top  of  it  another  carrier, 
until  all  are  represented.  Then  the  pile  is  shoveled  over  and 
over,  and  finally  leveled  and  the  process  repeated  until  the 
ingredients  are  thoroughly  mixed.  This  lot  of  fertilizer 
is  then  put  in  sacks  and  the  operation  repeated  with  another 
quantity  until  a  sufficient  amount  is  prepared.  There 
should  always  be  two  hundred  pounds  or  more  of  filler  in 
each  ton  to  give  a  more  uniform  distribution  of  the  carriers. 

QUESTIONS 

1.  In  what  parts  of  the  United  States  are  fertilizers  used  in 
greatest  quantities  ? 

2.  What  is  meant  by  a  brand  of  fertilizer  ? 


206  SOILS   AND   FERTILIZERS 

3.  What  is  a  high-grade  in  distinction  from  a  low-grade  fertilizer  ? 

4.  Explain  what  is  meant  by  a  filler. 

5.  What,  in  a  general  way,  does  a  report  on  the  inspection  of  a 
fertilizer  show  ? 

6.  How  are  trade  values  of  plant  nutrients  evaluated  ? 

7.  What  are  the  advantages  to  be  derived  from  the  home  mixing 
of  fertilizers  ? 

LABORATORY   EXERCISES 

Exercise  I.  —  Fertilizer  inspection  and  control. 

Fertilizer  laws  are  designed  to  protect  the  honest  manufacturer 
as  well  as  the  farmer.  Obtain  the  laws  of  your  state  which  have  to 
do  with  fertilizer  inspection  and  control.  Analyze  them  step  by 
step  with  this  point  always  in  mind.  Decide  whether  or  not  the 
law  does  really  regulate  and  protect  in  the  way  that  it  should.  A 
study  of  fertilizer  bags  and  tags  could  also  be  made  with  profit. 

Exercise  II.  —  Laboratory  mixture  of  fertilizers. 

Materials.  —  Sodium  nitrate,  dried  blood,  acid  phosphate, 
muriate  of  potash,  sulfate  of  potash,  balances,  dry  soil  as  a  filler. 
You  must  have  the  guaranteed  composition  of  each  carrier. 

Procedure.  —  Make  2000-gram  lots  of  the  following  mixtures. 
Fertilizers  must  be  dry  and  fine.     Put  through  sieve  if  necessary. 

No.  1.  —  Make  up  2  kilos  of  a  3-7-10  fertilizer,  using  sodium 
nitrate,  acid  phosphate  and  muriate  of  potash.  Add  filler  as  nec- 
essary. 

No.  2.  —  Make  up  a  fertilizer  as  above,  using  dried  blood,  acid 
phosphate  and  sulfate  of  potash. 

Allow  these  mixtures  to  stand  for  some  weeks  and  compare. 
Also  compare  them  as  to  physical  condition  with  a  ready  mixed 
fertilizer  of  a  similar  guarantee. 

Exercise  III.  —  Home  mixture  of  fertilizers. 

If  possible  cooperate  with  some  farmer  in  the  mixing  of  fertilizers. 
Allow  the  pupils  to  check  all  calculations  and  to  aid  in  the  actual 
mixing  of  the  goods.  The  pupils  should  also  understand  the  pro- 
cedure of  selecting  and  ordering  the  fertilizer  carriers  in  order  that 
every  step  in  the  process  may  be  familiar  to  them.  The  educational 
value  of  a  study  of  the  crop,  soil,  fertilizer  and  rotation  is  a  strong 
point  in  favor  of  home  mixing. 


CHAPTER  XVI 

THE   USE  OF  FERTILIZERS 

We  have  seen  that  a  very  considerable  economy  in  the 
purchase  of  fertilizers  may  be  effected  through  a  knowledge 
of  their  composition.  There  is  still  further  opportunity 
for  both  economy  and  profit  through  a  study  of  their  use. 

261.  Fertilizers  for  different  crops.  —  It  has  already  been 
pointed  out  that  there  is  a  difference  in  the  ability  of  plants  of 
different  kinds  to  extract  nutriment  from  the  soil.  Some 
crops  are  able  to  draw  abundant  nourishment  from  soils 
from  which  others  derive  but  little.  This  may  be  due,  in 
part,  to  (1)  a  deficiency  in  the  soil  of  the  particular  sub- 
stance most  greatly  needed  b,y  the  crops,  or  (2)  the  inherent 
ability  of  one  crop  to  make  available  plant-food  materials, 
while  another  crop  may  possess  that  quality  in  much  less 
degree.  There  are  therefore  two  ultimate  considerations 
in  the  selection  of  fertilizers :  (1)  the  nature  of  the  soil ; 
(2)  the  kind  of  crop.  The  second  of  these  will  be  discussed 
first. 

262.  Small  grains.  —  Most  of  the  small  grains,  like  wheat, 
rye,  oats  and  barley,  need  the  principal  part  of  their  nitrogen 
early  in  the  season,  before  the  soil  has  warmed  sufficiently 
to  induce  the  germs  that  produce  nitrates  to  lay  up  an  abun- 
dant supply.  Consequently  the  application  of  nitrate  of  \ 
soda,  when  growth  begins  in  the  spring,  is  very  beneficial 
to  these  crops.  Wheat  in  particular  needs  such  an  appli- 
cation. Since  it  is  a  "  delicate  feeder  "  it  grows  best  after 
fallow,  or  a  cultivated  crop,  and  when  it  follows  oats,  as  is 

207 


208  SOILS  AND   FERTILIZERS 

the  usual  custom,  it  needs  a  complete  fertilizer.  Rye  is  a 
"  stronger  feeder  "  and  does  not  have  the  same  need  of 
fertilization.  Oats  and  barley,  when  spring  sown,  find  more 
nitrates  in  the  soil,  because  they  are  later  than  winter 
wheat  in  starting  growth,  and,  as  they  can  make  better  use 
of  the  soil  fertility,  they  do  not  require  so  much  fertilizing. 

Corn  is  a  "  strong  feeder,"  and,  while  it  removes  a  very 
large  quantity  of  plant-food  materials  from  the  soil,  it  does 
not  require  that  these  be  added  in  a  soluble  form.  Farm 
manure  and  slowly  acting  fertilizers  may  well  be  used  for  the 
corn  crop.  The  long  growing  period  required  by  the  corn 
plant  gives  it  opportunity  to  utilize  nitrogen  as  that  sub- 
stance becomes  available  during  the  summer,  when  nitrate 
formation  is  most  active.  Phosphoric  acid  is  the  substance 
usually  most  needed  by  corn. 

263.  Grass  crops.  —  Meadows  and  pastures  are  greatly 
benefited  by  fertilizers.  The  grasses  are  less  vigorous  feed- 
ers than  the  cereals,  have  shorter  roots,  and,  when  left  down 
for  a  year  or  more,  the  formation  of  nitrates  is  much  curtailed. 
There  is  usually  a  more  active  fixation  of  nitrogen  in  grass 
land  than  in  cultivated  land,  but  nitrogen  thus  acquired 
becomes  available  very  slowly.  Different  soils  and  different 
climatic  conditions  necessitate  different  methods  of  manur- 
ing for  grass.  The  use  of  nitrate  is  almost  always  attended 
with  much  success,  even  when  used  alone,  but  in  most  situa- 
tions a  complete  fertilizer  is  profitable. 

264.  Leguminous  crops.  —  Most  of  the  leguminous  crops 
are  deep-rooted  and  are  vigorous  "  feeders."  Their  ability 
to  acquire  nitrogen  from  the  air  makes  the  use  of  that  sub- 
stance unnecessary  except  in  the  form  of  nitrate,  which  is 
often  very  effective  in  starting  a  young  seeding  of  alfalfa. 
The  nitrate  probably  serves  to  carry  the  young  crop  through 
the  period  preceding  the  development  of  tubercles.  Potash 
salts  are  almost  always  profitably  used  on  legumes,  and 


THE    USE  OF   FERTILIZERS  209 

phosphoric  acid  is  also  likely  to  be  effective.  For  such 
crops  as  clover  and  alfalfa  there  should  always  be  an  ample 
supply  of  lime,  without  which  these  crops  cannot  be  prof- 
itably grown. 

265.  Root  crops.  —  Most  of  the  root  crops  remove  very 
large  quantities  of  plant-food  materials  from  the  soil,  when 
these  are  present  in  available  form.  Like  corn  they  have  a 
long  growing  season  and  the  slowly  acting  fertilizers  or  farm 
manure  are  well  adapted  to  their  use.  A  complete  fertilizer 
in  rather  large  quantity  will  usually  bring  a  response  in 
yield.  For  sugar  beets  the  proportion  of  potash  should  be 
high,  and  for  table  beets  and  carrots  there  should  be  more 
nitrogen  than  for  the  other  roots. 

266.  Vegetables.  —  In  raising  some  kinds  of  vegetables, 
the  object  is  to  produce  a  rapid  growth  of  leaves  and  stalks 
rather  than  fruit  or  seeds,  and  with  these  kinds  growth  should 
often  be  made  in  the  early  spring.  Therefore,  for  crops 
like  lettuce,  radishes  and  asparagus  a  soluble  form  of  nitro- 
gen is  very  desirable.  For  crops  that  are  raised  later 
in  the  season  a  smaller  proportion  of  nitrogen  may  be  used, 
and  for  the  more  slowly  growing  kinds  of  vegetables  the  less 
soluble  fertilizers  may  be  applied.  For  all  vegetables  farm 
manure  or  other  organic  manure  should  be  generously  used, 
as  it  keeps  the  soil  in  a  mechanical  condition  favorable  to 
retention  of  moisture,  which  vegetables  require  in  large 
quantities,  and  it  also  supplies  needed  fertility.  The  very 
intensive  culture  employed  in  the  production  of  vegetables 
necessitates  the  use  of  much  greater  quantities  of  fertilizers 
and  farm  manure  than  are  used  for  field  crops,  and  the  great 
value  of  the  product  justifies  the  practice. 

267.  Orchards.  —  In  manuring  orchards,  it  is  the  aim 
to  maintain  a  continuous  supply  of  nutrients  available  to 
the  plants,  but  not  sufficient  for  stimulation,  except  during 
the  early  life  of  the  tree,  when  rapid  growth  of  wood  is 


210 


SOILS   AND   FERTILIZERS 


desired.  During  the  first  few  years  after  setting  out,  there 
should  be  a  liberal  supply  of  nitrogen.  An  acre  of  apple 
trees  in  bearing  removes  as  much  plant-food  material  from 
the  soil  in  one  season  as  does  an  acre  of  wheat.  Green- 
manures  may  be  used  to  advantage  in  orchards,  as  by  plant- 
ing these  crops  in  midsummer,  moisture  is  removed  from 
the  soil  and  the  wood  of  the  trees  is  thereby  hardened  and 
thus  prepared  to  withstand  the  low  temperatures  of  winter. 
The  green-manures  also  hold  snow  on  the  ground,  if  allowed 
to  stand  over  winter,  and  may  then  be  plowed  under  in  the 
spring. 

268.  Fertilizer  mixtures  for  different  crops.  —  On  ac- 
count of  the  large  number  of  factors  that  enter  into  the  pro- 
cesses of  crop  production,  it  is  obviously  impossible  to  pre- 
scribe accurately  the  proportion  and  quantity  of  fertilizer 
carriers  that  should  be  applied.  Some  rough  approximation 
can,  however,  be  arrived  at  on  the  basis  of  the  peculiarities 
of  the  various  classes  of  crops  that  have  just  been  enumerated. 
It  must  be  remembered  that  different  soil  conditions  may 
materially  change  the  proportions  of  the  fertilizer  ingredi- 
ents that  should  be  applied.  The  following  proportions  of 
nitrogen,  phosphoric  acid  and  potash  for  different  classes 
of  crops  have  been  proposed  and  have  been  found  a  fairly 
useful  guide  in  the  home  mixing  of  fertilizers. 

Table  43.  —  Fertilizer  Formulas  for  Different  Crops 


Crops 

Percentage 

of 

Nitrogen 

Percentage 

of  Phosphoric 

Acid 

Percentage 
of 
Potash 

Legumes  (young)    .... 

Small  grains        

Vegetables 

Grass 

Orchard     

Roots 

1 

3 
4 
5 
4 
3 

8 
8 
8 
4 
8 
8 

10 
5 

10 
4 
6 

7 

THE    USE   OF   FERTILIZERS  211 

A  fertilizer  based  on  the  first  percentages  would  be  called 
a  1-8-10  fertilizer ;  one  based  on  the  second  a  3-8-5  ferti- 
lizer, and  so  on.  In  making  up  these  formulas  the  carriers 
to  use  are  indicated  in  the  previous  discussion.  The  quan- 
tities that  it  is  desirable  to  use  will  depend  so  much  on 
the  natural  productiveness  of  the  soil  that  it  is  not  possible 
to  prescribe  for  soils  in  general.  On  soils  of  about  average 
productiveness,  however,  a  certain  range  for  each  of  the 
classes  of  crops  may  be  suggested. 

Legumes  .     .  100  to    200  pounds  per  acre 

Small  grains 100  to    300  pounds  per  acre 

Vegetables 500  to  1000  pounds  per  acre 

Grass 200  to    500  pounds  per  acre 

Orchards 200  to    600  pounds  per  acre 

Roots        . 300  to    800  pounds  per  acre 

269.  Fertilizers  for  different  soils.  —  The  best  way  to 
ascertain  what  fertilizers  are  needed  for  a  particular  soil  is 
to  test  it  with  different  kinds  and  quantities  of  fertilizing  ma- 
terials. It  will  thus  be  possible  to  estimate  whether  the 
three  substances,  nitrogen,  phosphoric  acid  and  potash 
are  all  needed,  and  in  about  what  quantities  they  should 
be  applied. 

A  practical  way  is  to  select  a  level  and  apparently  uniform 
part  of  a  field  and  on  it  lay  off  plats  of  land  eight  rods  long 
and  one  rod  wide,  giving  an  area  of  ^  of  an  acre.  These 
plats  should  lie  parallel  on  their  long  side,  but  should  have 
a  space  of  at  least  three  feet  between  them.  The  arrange- 
ment is  shown  in  Fig.  31  on  the  next  page,  which  also  in- 
dicates the  quantity  of  fertilizing  substance  that  each  plat 
should  receive. 

The  fertilizer  used  in  this  experiment  is  designed  for  small 
grains,  the  mixture  being  3-8-5  if  the  carriers  contain  about 
15  percent  nitrogen,  14  percent  phosphoric  acid  and  48  per- 
cent potash  respectively.     If   a  legume  or  grass  crop   is 


212  SOILS   AND   FERTILIZERS 

used  in  the  test  the  fertilizer  should  be  adjusted  to  suit  the 
crop,  as  stated  in  Table  43.     If  grass  is  the  most  important 


No  fertilizer 


Nitrate  of  soda  5  pounds 

Acid  phosphate  15  pounds 


Nitrate  of  soda  5  pounds 

Muriate  of  potash     2\  pounds 


No  fertilizer 


Acid  phosphate  15  pounds 

Muriate  of  potash     2\  pounds 


Nitrate  of  soda  5  pounds 

Acid  phosphate  15  pounds 

Muriate  of  potash     2|  pounds 


No  fertilizer 


Nitrate  of  soda  2\  pounds 

Acid  phosphate         1\  pounds 
Muriate  of  potash       1  pound 


Fig.  31.  —  Plan  for  a  fertilizer  experiment  with  small  grains.  Plats  of  land 
8  rods  long  and  1  rod  wide,  giving  an  area  of  fa  acre  in  each  plat.  The  rate 
of  application  to  the  acre  would  therefore  be  twenty  times  the  quantities  given 
in  the  diagram. 

crop  the  test  should  be  made  with  special  reference  to  it, 
and  so  with  any  other  important  crop.     In  any  case  a  ro- 


Plate  XIII.  Crop  Work.  —  The  upper  figure  shows  a  plat  of  timothy 
the  left-hand  side  of  which  has  been  properly  fertilized.  The  right-hand 
side  has  received  no  fertilizer.  Note  the  thick  stand  of  daisies  on  the 
latter. 

The  lower  figure  illustrates  the  method  of  laying  off  plats  for  tests  of 
fertilizers. 


THE    USE   OF   FERTILIZERS  213 

tation  should  be  followed  and  the  system  of  fertilization  should 
be  adjusted  to  the  rotation  as  explained  in  §  271. 

In  order  that  the  kind  and  quantity  of  fertilizer  shall  be  a  con- 
trolling factor,  the  plats  should  be  well  drained  and  well  tilled 
and  should  not  be  in  need  of  lime,  which  may  be  ascertained 
by  either  of  the  tests  described  in  §§  145,  146. 

270.  Calculation  of  the  results.  —  Each  test  plat  has,  on 
one  side  of  it,  a  plat  that  has  not  been  fertilized.  The  non- 
fertilized  or  check  plats  will  not  all  give  the  same  yield  be- 
cause the  soil  differs  in  various  parts  of  the  field.  If  the 
variations  in  yield  between  check  plats  are  not  greater  than 
one  bushel  to  the  acre,  they  may  be  considered  as  being  equal. 
If  a  greater  difference  exists,  the  yield  from  each  check  plat 
must  be  subtracted  from  the  yields  of  the  test  plats  beside 
it  and  the  result  may  then  be  considered  to  be  the  increase 
due  to  the  fertilizer  application. 

If  the  yield  is  as  good,  or  nearly  as  good,  on  a  check  plat 
as  it  is  on  the  corresponding  test  plat  that  lacks  one  of  the 
fertilizing  constituents,  it  may  be  concluded  that  the  use  of 
that  constituent  would  not  be  a  profitable  investment.  On 
the  other  hand,  the  very  beneficial  substances  will  be  indi- 
cated by  the  increased  yields  wherever  they  are  used.  Fi- 
nally the  desirable  quantities  will  be  indicated  by  a  compari- 
son of  the  rates  of  increase  on  the  plats  receiving  the  full 
quantity  and  those  receiving  the  half  quantity  of  complete 
fertilizer.  The  tests  should  be  continued  for  a  period  of 
three  to  five  years  in  order  that  they  shall  be  indicative  of 
the  fertilizer  needs  of  the  soil,  and  a  rotation  of  crops  should 
be  used,  with  an  adjustment  of  the  fertilizer  treatments  to 
suit  the  different  crops. 

271.  Fertilizing  the  rotation.  —  In  a  rotation  of  crops 
fertilizers  need  not  be  applied  every  year.  For  instance  a 
rotation  consisting  of  hay,  two  or  three  years,  corn,  oats 
and  wheat  would  probably  not  receive  any  fertilizers  on 


214  SOILS   AND   FERTILIZERS 

one  or  two  of  the  courses.  It  is  desirable  to  make  the  rela- 
tively heaviest  applications  for  the  crops  having  the  greatest 
money  value.  If  the  hay  crop  represents  the  largest  pos- 
sible returns,  the  crop  should  be  well  fertilized.  Another 
reason  for  giving  liberal  applications  to  the  hay  crop  is  that 
the  sod  is  thereby  increased  and  furnishes  a  larger  supply 
of  organic  matter  to  be  plowed  under  (see  §  204).  Corn 
is  the  crop  of  greatest  importance  in  some  localities,  in 
which  case  it  should  be  well  fertilized.  Farm  manure  is 
usually  the  best  fertilizer  for  corn,  but  farm  manure  should 
be  supplemented  by  phosphoric  acid  either  in  the  form  of 
acid  phosphate,  basic  slag  or  floats.  Oats  will  seldom  give 
a  profitable  response  to  fertilizers  which  may  be  dispensed 
with  for  that  crop,  but  should  be  applied  in  the  fall  in  prep- 
aration for  wheat.  It  is  hardly  necessary  to  say  that  winter 
wheat  should  have  the  nitrogen  applied  in  the  spring  in  the 
form  of  nitrate  of  soda,  while  the  phosphoric  acid  and  potash 
should  be  harrowed  in  before  planting. 

272.  Methods  of  applying  fertilizers.  —  The  distribution 
of  fertilizers  by  means  of  machinery  is  much  more  satis- 
factory than  is  broadcasting  by  hand,  because  the  former 
method  gives  a  more  uniform  distribution.  Cereal  and 
other  crops  are  now  usually  planted  with  a  drill,  or  a  planter 
provided  with  an  attachment  for  dropping  the  fertilizer  at 
the  same  time  that  the  seed  is  sown,  the  fertilizer  being,  by 
this  method,  placed  under  the  surface  of  the  soil.  Broad- 
casting machines  are  also  used,  which  leave  the  fertilizer 
uniformly  distributed  on  the  surface  of  the  ground,  thus  per- 
mitting it  to  be  applied  and  harrowed  in  a  sufficient  time 
before  the  seed  is  planted  to  prevent  injury  to  the  seed 
through  the  chemical  activity  of  the  fertilizer. 

Corn-planters  with  fertilizer  attachment  deposit  the  ferti- 
lizer beneath  the  seed,  so  as  not  to  bring  the  two  in  contact. 
Grain  drills  do  not  do  this  and  if  the  quantity  of  fertilizer 


THE    USE  OF   FERTILIZERS  215 

exceeds  300  or  400  pounds  to  the  acre,  it  is  better  to  apply 
it  before  seeding.  Grass  seed  and  other  small  seeds  should 
be  planted  only  after  the  fertilizer  has  been  mixed  with  the 
soil  for  several  days. 

273.  The  limiting  factor.  —  Attention  has  been  called  to 
the  important  influence  that  any  condition  unfavorable  to 
plant  growth  is  sure  to  exercise  in  curtailing  yield  of  crops. 
If  poor  drainage  is  the  difficulty,  crop  yields  may  be  reduced 
to  almost  nothing,  while  if  this  be  corrected  a  very  productive 
piece  of  land  may  result.  The  same  principle  holds  true 
when  there  is  a  deficiency  of  any  one  of  the  fertilizing  sub- 
stances. There  may  be  present  in  a  soil  an  abundant  supply 
of  available  phosphoric  acid  and  potash,  but  if  nitrogen  is 
deficient  the  crop  yield  is  limited  to  the  size  of  crop  that  the 
quantity  of  available  nitrogen  present  will  produce.  Each 
of  the  essential  plant-food  materials  exercises  this  control. 
It  is,  therefore,  a  requisite  in  the  economical  use  of  ferti- 
lizers to  have  a  well-balanced  mixture  of  plant  nutrients. 
The  balance  must  be  adjusted  to  the  needs  of  each  partic- 
ular soil,  and  to  each  kind  of  crop.  Of  course  it  is  impossible 
to  work  out  any  fertilizer  mixture  that  will  fit  these  condi- 
tions exactly.  These  relationships  are  best  worked  out  by 
field  tests  with  fertilizer  mixtures  (see  §  269). 

274.  The  law  of  diminishing  returns.  —  A  small  applica- 
tion of  fertilizer  usually  effects  a  greater  percentage  increase 
of  crop  than  does  a  larger  application.  This  is  unfortu- 
nate, because  it  means  that  there  is  a  limit  to  the  profit- 
able use  of  fertilizers,  for  although  the  cost  of  the  fertilizer 
rises  in  direct  proportion  to  the  quantity  used,  the  rate  of 
yield  decreases  after  a  certain  point  has  been  reached,  and 
consequently  the  value  of  the  product  finally  becomes  less 
than  the  cost  of  the  fertilizer.  This  law  of  diminishing 
returns  may  be  illustrated  by  an  experiment  in  which  floats 
were  applied  in  several  different  quantities  to  plats  of  land, 


216 


SOILS   AND   FERTILIZERS 


each  of  which  plats  also  received  an  application  of  farm  ma- 
nure at  the  rate  of  15  tons  an  acre.  The  applications  of 
floats  were  at  the  rate  of  200,  400, -800  and  2400  pounds  to 
the  acre  respectively.  In  the  following  table  are  stated  the 
increased  yields  over  the  check  plats  receiving  the  same 
quantity  of  farm  manure  but  no  floats.  The  values  of 
the  crops  and  cost  of  floats  are  reckoned  on  the  same  basis. 

Table  44.  —  Increased  Yields  and  Values  op  Corn  Resulting 
from  Application  of  Farm  Manure  and  Floats 


Fertilizer  Treatment  per  Acre 

Grain 

BU. 

Value 

Cost  of 
Floats 

Difference 

15  tons  of  manure  +  200  lbs. 
floats     

7.0 

$4.62 
5.48 
6.73 
8.38 

$  0.90 

1.80 

3.60 

10.80 

$3.72 

15  tons  of  manure  +  400  lbs. 
floats     

8.3 

3.68 

15  tons  of  manure  +  800  lbs. 
floats     

10.2 

3.13 

15  tons  of  manure  +  2400  lbs. 
floats      

12.7 

2.42  loss 

It  may  be  seen  that  the  increase  from  the  use  of  the  first 
200  pounds  of  floats  was  greater  than  from  the  additional  200 
pounds,  and  from  the  next  400  pounds  the  increase  was  at 
a  still  lower  rate.  This  is  best  shown  by  a  curve,  which  may 
be  seen  in  the  upper  part  of  Fig.  32. 

From  the  direction  taken  by  the  curve  it  may  be  seen  that 
finally  a  point  will  be  reached  when  there  will  no  longer  be 
any  increase  from  larger  applications  of  fertilizer.  Long 
before  that  point  is  reached,  however,  the  use  of  the  ferti- 
lizer ceases  to  be  profitable.  This  may  be  shown  by  another 
diagram  containing  curves  for  the  value  of  the  grain  and  the 
cost  of  the  fertilizer.     (See  lower  diagram  in  Fig.  32.) 

This  diagram  as  well  as  the  last  column  of  Table  44  shows 
that  the  difference  between  the  value  of  the  product  and  the 


THE    USE   OF   FERTILIZERS 


217 


cost  of  the  fertilizer  decreases  after  the  lowest  application,  and 
that  for  the  very  heavy  application  there  is  an  actual  loss. 

275.    Conditions  that  influence  the  effect  of  fertilizers.  — 
The  extent  to  which  fertilizers  are  utilized  by  crops  depends 


is 


44 

\o 

sc 

o 

/z 

6b 

Ye>oo 

zooo 

Z440 

POUHDS    OF    FLOATS     APPLIED  PER.     X7CRE 


pounos 


800  /200 

OF  PLOPT5    APPLIED 


/600  2000 

PER  PCR.E 


34W 


Fig.  32.  —  In  the  upper  diagram  the  heavy  line  shows  how  the  yields  of 
corn  were  increased  by  graduated  applications  of  phosphoric  acid  in  floats. 
It  will  be  seen  that  the  increases  in  yields  were  proportionately  much  greater 
for  small  applications  than  for  large. 

The  lower  diagram  illustrates  the  rate  at  which  the  cost  of  the  fertilizer 
approaches  and  finally  passes  the  value  of  the  product  as  the  size  of  the  appli- 
cation increases. 

on  the  presence  or  absence  of  certain  conditions.  The  entire 
amount  of  any  constituent  of  a  fertilizer  is  never  recovered  by  a 
crop  in  any  one  year.  This  is  a  very  important  consideration 
in  the  manuring  of  land,  for  under  conditions  as  they  fre- 
quently exist,  the  use  of  fertilizers  is  wasteful  and  extravagant. 


218  SOILS  AND   FERTILIZERS 

The  factors,  within  the  control  of  man,  that  affect  the 
availability  of  fertilizers  are  the  following :  (1)  the  kind  of 
crops  ;  (2)  soil  moisture  content ;  (3)  soil  acidity ;  (4)  tilth 
of  the  soil ;  (5)  organic  matter  in  the  soil. 

An  undesirable  condition  of  any  one  or  more  of  these 
factors  is  a  very  common  occurrence,  and  yet  fertilizers  are 
expected  to  produce  profitable  returns,  in  spite  of  these 
adverse  conditions.  It  must  be  remembered  that  the  supply 
of  nutrients  is  only  one  of  the  conditions  that  influence  plant 
growth.  Furthermore,  an  economical  use  of  fertilizers 
requires  that  they  merely  supplement  the  natural  supply 
of  plant  nutrients  in  the  soil,  and  that  the  latter  should  fur- 
nish the  larger  part  of  the  nutrient  material  used  by  the 
crop.  Finally,  most  fertilizers  are  rendered  less  readily 
soluble  by  the  absorptive  properties  of  the  soil,  and  the  re- 
lease of  these  substances  for  plant  use  depends  to  a  great 
extent  on  the  conditions  enumerated  above. 

276.  Response  of  sandy  and  of  clay  soils  to  fertilizers.  — 
It  is  generally  recognized  that  a  sandy  soil  responds  more 
promptly  to  the  application  of  fertilizers  than  does  a  clay 
soil.  There  are  probably  two  reasons  for  this  :  (1)  Absorp- 
tion may  not  be  so  complete  both  on  account  of  the  particles 
being  larger,  and  because  in  many  sandy  soils  the  particles 
are  largely  composed  of  quartz,  which  does  not  have  the 
property  of  forming  combinations  with  bases,  as  does  clay; 
(2)  Drainage  and  aeration  are  likely  to  be  better,  as  are  most 
of  those  conditions  that  make  plant-food  materials  more 
available.  For  these  reasons,  a  sandy  soil  generally  makes 
a  greater  response  to  fertilizers  the  first  year,  but  shows  less 
effect  in  subsequent  years  unless  the  treatment  is  repeated. 
On  the  other  hand,  less  fertilizing  material  is  lost  from  a  clay 
soil  by  leaching. 

277.  Cumulative  need  for  fertilizers.  —  It  is  often  re- 
marked that  on  land  habitually  fertilized  there  is  a  gradually 


}  , 

i     Si— : : s | 

J 

1- 

1 

l 

l 

«    i 

1       J 

1     X 

\,  "■'/ 

/|Hj 

iy  •  iiv- 

fixi 

,w%nk 

:m$k 

[Hu  \  ^^^J 

Wm 

H 

A  sufficient  supply  of  moisture  makes  a  fertilizer  more  effective.    Note 
the  greater  response  to  fertilization  in  the  vessels  having  more  moisture. 


Vessel  45.  Moisture  30  per  cent, 

Vessel  49.  Moisture  15  per  cent, 

Vessel  58.  Moisture  30  per  cent, 

Vessel  64.  Moisture  15  per  cent, 

Vessel  69.  Moisture  30  per  cent. 

Vessel  78.  Moisture  15  per  cent, 


no  fertilizer, 
no  fertilizer, 
complete  fertilizer, 
complete  fertilizer, 
more  fertilizer, 
more  fertilizer. 


Plate  XIV,  —  A  soil  may  contain  too  much  or  too  little  moisture.   The 
best  crop  is  in  the  vessel  having  next  to  the  largest  quantity  of  water. 

Vessel  20.    Moisture  11  per  cent.  Vessel  26.    Moisture  25  per  cent. 

Vessel  22.    Moisture  13  per  cent.  Vessel  28.    Moisture  38  per  cent. 

Vessel  24.    Moisture  20  per  cent.  Vessel  32.    Moisture  45  per  cent. 


THE    USE    OF    FERTILIZERS  219 

increasing  need  for  greater  quantities  of  fertilizers.  This  is 
doubtless  the  case  in  many  instances,  and  arises  from  neglect 
of  other  factors  affecting  soil  productiveness.  As  we  have 
seen,  certain  fertilizers  cause  the  soil  to  lose  lime,  which 
results  in  soil  acidity.  Organic  matter  is  allowed  to  decrease, 
and  this  causes  the  soil  to  become  compact  and  poorly  aerated, 
and  thus,  one  bad  condition  leads  to  another  and  crops  be- 
come poorer  in  spite  of  increased  applications  of  fertilizer. 

QUESTIONS 

1.  Why  are  some  crops  able  to  draw  abundant  nourishment  from 
soils  on  which  other  crops  yield  poorly  ? 

2.  How  do  wheat  and  corn  differ  in  their  need  of  plant-food 
materials  ? 

3.  Why  is  nitrate  of  soda  particularly  beneficial  to  grass  ? 

4.  What  two  fertilizer  materials  are  generally  useful  on  legumes  ? 

5.  What  fertilizer  material  is  required  in  large  amounts  by  most 
root  crops  ? 

6.  What  plant  nutrient  is  especially  needed  by  vegetables  that 
are  expected  to  make  a  rapid  and  succulent  growth  ? 

7.  In  what  ways  are  green-manures  of  use  in  orchards  ? 

8.  Plan  a  fertilizer  test  similar  to  that  shown  in  Pig.  31,  but 
to  be  used  with  a  crop  of  timothy  instead  of  small  grain. 

9.  To  what  crops  in  a  rotation  of  corn,  oats,  wheat,  and  grass 
would  you  apply  fertilizers  ? 

10.  Explain  what  is  meant  by  the  limiting  factor  in  plant  growth 
with  respect  to  the  use  of  fertilizers. 

11.  What  is  meant  by  the  law  of  diminishing  returns  ? 

12.  Name  five  soil  factors  within  the  control  of  man  that  influ- 
ence the  availability  of  fertilizers. 

13.  Give  two  reasons  why  a  sandy  soil  responds  more  promptly 
to  fertilizers  than  does  a  clay  soil. 

14.  Explain  why  soils  sometimes  demand  an  increasing  use  of 
fertilizers  to  maintain  their  productiveness. 

LABORATORY   EXERCISES 

Exercise  I.  —  Fertilization  of  standard  rotations. 
The  fertilization  of  the  rotation  is  the  ultimate  and  final  consider- 
ation of  any  systematic  use  of  fertilizers.     While  the  fertilization  as 


220  SOILS   AND   FERTILIZERS 

to  amounts  and  mixtures  is  generally  different  for  different  farms, 
the  place  of  fertilizers  in  a  standard  rotation  is  more  or  less  fixed. 

Take  a  number  of  good  practical  rotations  and  indicate  where  in 
the  succession  of  crops  the  fertilization  should  occur.  Also  suggest 
what  should  be  the  formula  of  each  mixture  used,  the  fertilizer 
compounds  which  should  be  carried  and  the  amounts  that  might 
be  applied  to  a  given  soil. 

Exercise  II.  —  Fertilization  of  home-farms. 

Encourage  the  pupils  to  bring  in  data  regarding  the  fertilization 
on  their  home  farms.  Tabulate,  discuss  and  criticize  such  data  in 
a  practical  way.  If  any  of  the  pupils  have  home  project  gardens, 
the  fertilization  of  such  gardens  should  be  made  a  special  problem 
for  them. 

Exercise  III.  —  Fertilizer  practice  in  the  community. 

A  fertilizer  survey  of  the  township  could  be  made  with  profit 
by  the  teacher,  visiting  each  farmer  and  making  inquiry  adequate 
for  the  purpose  in  view.  The  pupils  could  aid  not  only  in  the  col- 
lection of  such  data  but  also  in  such  compilation  and  interpreta- 
tion as  would  later  be  necessary. 

Taking  the  class  to  visit  a  farmer  whose  system  of  farming  and 
fertilization  is  a  practical  success  is  to  be  advocated.  The 
economic  use  of  fertilizers  is  attained  not  only  by  scientific  knowl- 
edge, but  also  by  good  sound  experience  and  practice. 

Exercise  IV.  —  Fertilizer  experimentation. 

The  measurement  in  crop  yield  of  the  effects  from  fertilizer  use  is 
the  only  true  means  of  gauging  fertilizer  needs  and  fertilizer  prac- 
tice.    Whether  a  certain  fertilizer  pays  is  the  ultimate  question. 

Jjay  out  plans  for  fertilizer  experimentation  as  suggested  in  the 
text  with  the  idea  of  taking  careful  data  as  to  crop  yield  from  the 
various  treatments  used  and  the  calculation  of  the  net  returns. 

The  fertilizer  needs  of  the  soil  for  nitrogen,  phosphoric  acid, 
potash  and  lime  may  be  determined  by  the  use  of  the  various  fer- 
tilizer carriers  both  alone  and  in  combination.  Different  ready  mixed 
fertilizers  may  also  be  compared.  The  amount  of  any  particular 
fertilizer  that  may  most  economically  be  used  can  be  tested  by  vary- 
ing the  applications  of  the  same  mixture.  The  relation  of  lime,  farm 
manure  and  time  of  application  to  the  effectiveness  of  any  particu- 
lar fertilizer  may  also  be  made  a  subject  of  experimentation. 


CHAPTER  XVII 
FARM  MANURES 

The  use  of  animal  manure  to  enrich  the  soil  antedates 
written  history,  and  it  is  still  the  most  commonly  and  widely 
used  fertilizer.  It  is  produced  on  nearly  every  farm.  Mar- 
ket-gardeners, who  usually  keep  few  animals,  buy  large  quan- 
tities of  horse  manure  from  cities.  Its  use  constitutes  a 
way  of  returning  to  the  land  a  part  of  the  plant  nutrients 
taken  up  by  crops,  as  well  as  replacing  some  of  the  or- 
ganic matter  destroyed  by  cultivation.  Farm  manure  con- 
tains nitrogen,  phosphoric  acid,  potash,  lime  and  the  other 
ingredients  removed  from  soils,  and  hence  is  a  direct  ferti- 
lizer. In  addition  to  these  it  contains  a  large  quantity 
of  organic  matter,  which  by  its  influence  on  tilth,  moisture 
and  absorptive  properties  is  a  valuable  soil  amendment,  and 
finally  it  favors,  in  a  number  of  ways,  a  vigorous  bacterial 
activity  that  does  much  to  bring  plant  nutrients  into  an 
available  condition. 

278.  Solid  and  liquid  manure.  —  Farm  manure  is  made 
up  of  the  solid  excreta  of  animals,  the  urine,  which  is  usually 
largely  absorbed  by  the  solid  ingredients,  and  the  litter 
used  for  bedding  the  animal.  As  these  constituents  differ 
greatly,  not  only  in  composition  but  also  in  physical  proper- 
ties, their  proportions  must  appreciably  affect  the  agri- 
cultural value  of  the  manure.  Litter  usually  does  not  have 
as  high  a  fertilizer  value  as  do  the  solid  and  liquid  excreta. 
Of  the  excreta  the  larger  part  is  solid  and  the  smaller  is 
urine.     The  ratios  may  be  found  in  Table  45.     The  propor- 

221 


222 


SOILS   AND   FERTILIZERS 


tion  of  litter  is  variable,  depending  on  the  extent  to  which 
bedding  is  used. 

279.  Chemical  composition  of  manures.  —  From  what 
has  already  been  said  regarding  the  variable  nature  of  ma- 
nure, it  will  be  understood  how  difficult  it  is  to  give  a  state- 
ment of  the  composition  of  a  representative  sample  of  ma- 
nure. The  following  table  gives  the  results  of  an  analysis 
that  may  be  considered  fairly  representative  of  mixed  fresh 
manure  from  several  different  classes  of  animals. 

Table  45.  —  Pounds  of  Water  and  Plant-Food  Materials  in 
One  Ton  of  Solid  Excreta,  One  Ton  of  Liquid  Excreta 
and  in  One  Ton  of  Entire  Excreta  of  Several  Different 
Classes  of  Animals 


Percentage  op  Solid  and  Liquid  Parts  of 
Excrement 


{Solid,  80  percent 
Liquid,  20  percent 
Entire  excreta     . 

{Solid,  70  percent 
Liquid,  30  percent 
Entire  excreta     . 


{Solid,  67  percent 
Liquid,  33  percent 
Entire  excreta     . 


{Solid,  60  percent 
Liquid,  40  percent 
Entire  excreta     . 


Pounds  in  a  Ton 


Water 


1500 
1800 
1560 

1700 
1840 
1720 

1200 
1700 
1360 

1600 
1940 
1740 


Nitro- 
gen 


11 

27 
14 

8 
20 
12 

15 

27 
19 

11 

8 
10 


Phos- 
phoric 
Acid 


6 

trace 

5 

4 

trace 

3 

10 
1 

7 

10 
2 

7 


Potash 


8 
25 
11 

2 

27 
9 

9 
42 
20 

8 
9 

8 


This  table  shows  that  the  solid  excrement  constitutes  by 
far  the  larger  part  of  the  total.  It  also  shows  that  a  ton  of 
liquid  excreta  is  generally  richer  in  nitrogen  and  potash  than 


FARM   MANURES 


223 


is  an  equal  quantity  of  solid  excrement,  but  in  the  case  of 
swine  there  is  little  difference  between  the  solid  and  liquid 
excreta  in  this  respect. 


TOTAL 

NITROGEN 

0.5% 


PHOSPHORIC 
ACID 
0.5% 


POTASH 
0.6% 


Fig.  33.  —  A  farm  manure  containing  0.5  percent  nitrogen,  0.3  percent 
phosphoric  acid  and  0.6  percent  potash  will,  on  the  average,  have  these 
constituents  divided  between  the  solid  and  liquid  parts  of  the  manure  in 
the  proportions  shown  above. 

280.  Farm  manure  an  unbalanced  fertilizer.  —  A  mix- 
ture of  horse  and  cow  manure,  with  an  ordinary  quantity 
of  straw  litter  will  have  a  composition  somewhat  as  follows : 


224 


SOILS  AND   FERTILIZERS 


Constituents 

Water 

Dry  matter 

Nitrogen 

Phosphoric  acid 

Potash 


Pounds 
Per  Ton 


1460 

540 

10 

5 

12 


Assuming  that  one-half  of  the  nitrogen,  one-fifth  of  the 
phosphoric  acid  and  one-half  of  the  potash  are  readily  avail- 
able, twenty  tons  of  mixed  manure  would  be  equivalent  to 
one  ton  of  a  5-1-6  fertilizer.  Comparing  this  with  any 
ordinary  fertilizer,  it  is  evident  that  it  is  high  in  nitrogen 
and  very  low  in  available  phosphoric  acid.  This  suggests 
that  for  its  most  effective  use  farm  manure  should  be  sup- 
plemented by  some  form  of  phosphoric  acid.  As  an  illustra- 
tion of  the  advantage  of  supplementing  farm  manure  by 
phosphoric  acid  see  Table  52. 

281.  Quantities  of  manure  voided  by  animals.  —  An  idea 
of  the  quantity  of  excreta,  solid  and  liquid,  produced  by 
different  animals  may  be  obtained  from  the  following  table  : 


Table  46. 


Excreta  from  Various  Farm  Animals  to  the  1000 
Pounds  Live  Weight 


Animal 

Pounds  per 

Day 

Tons  per  Year 

Horse          

50 
70 
40 
85 
34 

9.1 

Cow 

12.7 

Steer      

7.3 

Swine     .          

15.5 

Sheep 

6.2 

282.  Effect  of  food  on  composition  of  manure.  —  The 
richer  the  food  in  nitrogen  and  other  plant-food  materials, 
the  more  of  these  there  will  be  in  the  manure.     This  has 


FARM    MANURES 


225 


been  demonstrated  by  a  number  of  experiments,  from  which 
the  following  have  been  selected. 

Table  47.  —  Effect  of  Food  on  Composition  of  Animal  and 
Poultry  Manure 


Pounds  per  Ton  of  Manure 

Ration 

Nitrogen 

Phosphoric 
Acid 

Potash 

Fed  to  steers 

Corn  and  mixed  hay 

Corn,  oil  meal  and  hay      .... 

Corn,  oil  meal  and  clover       .     .     . 
Fed  to  fowls 

Nitrogenous  ration        

Carbonaceous  ration 

29.80 
31.00 
33.60 

16.00 
13.20 

10.53 
10.99 
11.91 

18.78 
14.65 

26.64 
24.48 
24.96 

6.48 
5.04 

283.  Commercial  evaluation  of  manures.  —  As  a  means 
of  comparing  manures,  they  may  be  evaluated  in  a  manner 
similar  to  that  used  with  commercial  fertilizers.  This, 
however,  fails  to  place  any  value  on  the  organic  matter, 
which  is  undoubtedly  of  much  benefit  to  the  soil.  In  the 
following  table  are  given  the  values  of  manures  produced 
by  different  animals  based,  in  part,  on  the  composition  given 
in  Table  45  when  the  nitrogen  is  considered  to  be  worth  ten 
cents  a  pound,  the  phosphoric  acid  two  and  one-half  cents 
and  the  potash  four  cents. 

Table  48.  —  Value   of   Excreta  Produced   by  Several 
Farm  Animals  « 


Animal 

Value  per  Ton 

Swine  excreta 

$1.50 

Cow  excreta 

1.64 

Horse  excreta 

1.97 

Sheep  excreta 

2.87 

Poultry  excreta 

4.80 

226 


SOILS   AND   FERTILIZERS 


If  the  mixed  horse  and  cow  manure  together  with  litter, 
similar  to  that  referred  to  in  section  280,  be  made  the 
basis  of  the  calculation,  the  evaluation  would  be  $1.60.  Dilu- 
tion of  the  plant-food  materials  due  to  the  litter  tends  to 
reduce  the  value. 

284.  Agricultural  evaluation  of  manures.  —  The  com- 
mercial value  may  be  quite  different  from  the  agricul- 
tural value,  which  is  calculated  from  the  increased  crop 
production  resulting  from  the  use  of  the  manure.  This 
will  vary  with  different  soils,  but  even  on  similar  soils  it 
will  vary  with  different  manures.  The  following  table  gives 
the  results  of  an  experiment  in  which  treated  and  untreated 
manures  were  evaluated  commercially  and  were  then  applied 
to  the  land.  The  value  of  the  increased  crops  in  a  three 
years'  rotation  was  then  calculated  in  terms  of  financial 
return  to  the  ton  of  manure  applied : 


Table   49.  —  Commercial   and   Agricultural   Evaluation   op 

Manures 


Manure 

Commercial. 
Value 

Agricultural 
Value 

Yard  manure  untreated    .... 
Yard  manure  plus  floats   .    -.     .     . 
Yard  manure  plus  acid  phosphate  . 
Yard  manure  plus  kainit        .     .     . 
Yard  manure  plus  gypsum     .     .     . 

$1.41 
2.04 
1.65 
1.45 
1.48 

$2.15 
3.31 
3.67 
2.79 
2.76 

285.  Deterioration  of  farm  manure.  —  There  is  always  a 
loss  in  the  value  of  farm  manure  on  standing.  The  ways 
in  which  this  is  brought  about  are:  (1)  fermentation;  (2) 
leaching.  The  first  of  these  is  a  natural  process,  common 
to  all  farm  manure  on  standing,  and  not  occasioned  by  any 
outside  agencies.     The  second  is  due  to  the  running  off  of 


Plate  XV.  Manures.  —  Farm  manure  is  becoming  relatively  more 
scarce  every  year.  Its  protection  is  becoming  more  essential  to  success- 
ful farming. 


FARM   MANURES  227 

the  liquid  portion  of  the  manure,  and  to  the  exposure  of  the 
manure  to  rain. 

286.  Fermentations  of  manure.  —  The  mixture  of  solid 
and  liquid  excreta  together  with  litter  used  as  bedding  con- 
stitutes a  wonderfully  favorable  material  for  the  growth  of 
bacteria,  the  number  of  which  frequently  amounts  to  many 
billion  in  a  gram  of  manure.  This  is  many  times  more 
than  are  found  in  soil.  It  is  then  small  wonder  that  fer- 
mentations proceed  at  a  prodigious  rate  in  a  manure  heap. 
These  fermentations  are  produced  both  by  bacteria  requiring 
oxygen  for  their  activity  and  by  those  that  need  little.  The 
fermentations  on  the  outside  of  the  heap  are  different  from 
those  on  the  inside,  where  air  does  not  readily  penetrate, 
but  as  fresh  manure  is  thrown  on  the  pile  from  day  to  day, 
most  of  the  manure  first  undergoes  fermentation  in  the  pres- 
ence of  air  and  afterwards  without  air. 

It  is  through  the  action  of  germs  on  the  nitrogenous  com- 
pounds of  manure  that  loss  of  value  through  fermentation 
occurs.  In  the  presence  of  air  ammonia  is  formed,  and  this 
being  in  a  volatile  form,  is  likely  to  escape.  The  drier  the 
heap,  the  more  likely  the  ammonia  is  to  escape. 

The  fermentations  in  the  interior  of  a  moist  manure  heap 
are,  in  the  main,  favorable  to  the  production  of  readily 
available  plant-food  material.  It  is  desirable  to  keep  the 
heap  as  compact  as  possible,  and  to  prevent  it  from  becom- 
ing dry  by  the  application  of  water  in  amounts  sufficient  to 
keep  the  heap  moderately  moist  without  leaching  it.  In 
the  arid  and  semi-arid  parts  of  the  country,  this  is  an  im- 
portant precaution  to  be  taken  in  the  preservation  of  farm 
manure. 

287.  Leaching  of  farm  manure.  —  When  water  is  allowed 
to  soak  through  a  manure  heap  and  to  drain  away  from  it, 
there  is  carried  off  in  solution,  and  to  some  extent  in  sus- 
pension, more  or  less  of  the  organic  matter  and  plant-food 


228 


SOILS   AND   FERTILIZERS 


materials  that  are  soluble  in  water  and  that  consequently 
represent  the  most  valuable  part  of  the  manure.  As  about 
one-half  of  the  nitrogen  and  two-thirds  of  the  potash  of  farm 
manure  is  in  a  soluble  condition,  the  possibility  of  loss  by 
leaching  is  very  great.  Even  phosphoric  acid  may  thus 
be  removed. 

It  is  rather  difficult  to  distinguish  between  the  losses  due 
to  fermentation  and  those  caused  by  leaching.  In  an  experi- 
ment conducted  in  Canada  a  carefully  mixed  quantity  of 
farm  manure  was  divided  into  two  parts,  one  of  which  was 
placed  in  a  bin  under  a  shed,  the  other  was  exposed  to  the 
weather  outside,  in  a  similar  bin.  After  a  year  the  two  por- 
tions were  analyzed  and  the  losses  thus  computed  are  stated 
in  the  following  table. 


Table  50. 


Losses  by  Fermentation  Alone  and  by  Fermen- 
tation and  Leaching  Combined 


Constituent  Lost 


Percentage  Loss 


Organic  matter 
Nitrogen     . 
Phosphoric  acid 
Potash   .     .     . 


288.  Protected  manure  more  effective.  —  Over  a  period 
•  of  fourteen  years,  in  a  three  year  rotation  of  corn,  wheat 
and  hay  at  the  Ohio  Experiment  Station,  stall  manure  gave 
an  average  yield  of  30  percent  more  than  did  equal  quantities 
of  yard  manure.  This  gives  a  fair  basis  on  which  to  cal- 
culate whether  it  would  pay  to  protect  the  manure  when  the 
expense  of  doing  so,  and  the  quantity  of  manure  produced, 
are  considered. 


FARM   MANURES 


229 


289.  Reinforcing  manure.  —  Various  substances  are  in- 
corporated with  animal  manures,  either  in  the  stall  or  in 
the  heap,  for  the  purposes  of  :  (1)  curtailing  loss  by  leaching 
and  fermentation,  and  (2)  balancing  the  manure  in  order  to 
better  adapt  it  to  the  needs  of  most  crops.  The  latter  has 
been  mentioned  in  section  280.  The  materials  commonly- 
used  for  these  purposes  are  gypsum,  kainit,  acid  phosphate 
and  floats. 

Experiments  at  the  Ohio  Experiment  Station  indicate  that 
the  conserving  effect  is  slight,  but  that  the  benefit  due  to 
reinforcing  is  considerable  when  acid  phosphate  or  floats 
are  used.  To  ascertain  the  conserving  properties  of  several 
substances,  each  was  mixed  with  the  manure  at  the  rate  of 
40  pounds  to  the  ton,  and  the  loss  of  fertilizing  value  was 
computed  from  analyses  after  the  mixtures  had  stood  from 
January  to  April.  The  results  are  shown  in  the  following 
table : 


Table  51. 


Effect  of  Reinforcing  Materials  on  Conserva- 
tion of  Fertility  in  Farm  Manure 


Materials  Used 

Value  of  Ton  of  Manure 

Percentage 

In  January 

In  April 

Loss 

None 

Gypsum 

Kainit - .     .     . 

Floats 

Acid  phosphate 

$2.19 
2.05 
2.24 
2.81 
2.34 

$1.41 
1.48 
1.45 
2.04 
1.65 

36 
38 
35 
24 
29 

The  actual  agricultural  value  of  the  reinforced  manure  was 
ascertained  from  tests  covering  a  period  of  fourteen  years 
in  a  rotation  of  corn,  wheat  and  hay,  of  which  the  results 
were  as  follows :, 


230  SOILS  AND   FERTILIZERS 

Table  52.  —  Financial  Results  of  Reinforcing  Farm  Manure 


Value  of  Net  In- 
creased Yield  to 
the   Ton  of  Manure 


Manure  alone        .... 
Manure  plus  gypsum      .     . 
Manure  plus  kainit    .     .     . 
Manure  plus  floats    .    . . 
Manure  plus  acid  phosphate 


$3.31 
3.56 
3.71 
4.49 

4.82 


It  has  already  been  remarked  that  farm  manure  is  deficient 
in  available  phosphoric  acid,  and  this  experiment  demon- 
.strates  the  benefit  to  be  gained  by  reinforcing  it  with  a  phos- 
phoric acid  fertilizer. 

290.  Methods  of  handling  manure.  —  The  least  oppor- 
tunity for  deterioration  of  farm  manure  occurs  when  it  is 
hauled  directly  to  the  field  from  the  stall  and  spread  at  once. 
Manure  may  even  be  spread  on  frozen  ground  or  on  snow, 
provided  the  land  is  fairly  level  and  the  snow  is  not  too  deep. 
However,  it  is  not  always  possible  to  follow  this  method  and 
manure  must  sometimes  be  stored.  In  the  storage  of  ma- 
nure the  two  important  conditions  are  a  sufficient  but  not 
an  excessive  supply  of  moisture,  and  a  well-compacted  mass. 
Water  draining  away  from  a  manure  heap,  and  a  fermenta- 
tion producing  a  white  appearance  of  the  manure  under  the 
surface  of  the  pile  ("  fire  fanging  "),  are  both  sure  indications 
of  unnecessary  loss  in  its  fertilizing  value. 

291.  Covered  barnyard.  —  The  best  method  of  storing 
manure  is  in  a  covered  yard  in  which  the  cattle  are  allowed  to 
exercise  and  thus  to  trample  and  compact  the  mixed  manure 
from  the  barn.  The  advantage  to  be  gained  from  the  tram- 
pling is  brought  out  by  some  Pennsylvania  experiments  in 
which  the  losses  of  fertilizing  constituents  were  compared 
when  the  covered  manure  was  trampled  and  when  it  was  not. 


FARM   MANURES 


231 


Table  53.  —  Loss  of  Fertilizing  Constituents  from  Farm 
Manure  in  Covered  Sheds  when  Trampled  and  when 
Not  Trampled 


Percentage  Loss  of 

Treatment  of  Manure 

Nitrogen 

Phosphoric 
Acid 

Potash 

Covered  and  trampled 

Covered  and  not  trampled    .     .    ■.     . 

5.7 
34.1 

5.5 
19.8 

8.5 
14.2 

292.  Application  of  manure  to  land.  —  In  applying  farm 
manure  to  the  field,  it  is  customary  either  to  throw  it  from 
the  wagon  in  small  heaps,  from  which  it  is  distributed  later, 
or  to  scatter  it  as  evenly  as  possible  immediately  on  hauling 
it  to  the  field.  The  use  of  the  automatic  manure-spreader 
accomplishes  the  latter  procedure  in  an  admirable  manner. 
As  between  these  two  methods,  the  advantage,  so  far  as  the 
conservation  of  fertility  is  concerned,  is  with  the  practice  of 
spreading  immediately.  When  piled  in  small  heaps,  fer- 
mentation goes  on  under  conditions  that  cannot  be  controlled, 
and  that  may  be  very  unfavorable.  The  heaps  may  dry 
out,  and  thus  lose  much  of  their  nitrogen,  or  they  are  likely 
to  leave  the  field  not  uniformly  fertilized  because  of  the 
leaching  of  some  of  the  constituents  of  the  manure  into  the 
soil  directly  under  and  adjacent  to  the  heap.  On  the  other 
hand,  when  spread  immediately,  little  fermentation  takes 
place,  as  the  manure  does  not  heat,  and  the  soluble  sub- 
stances are  leached  quite  uniformly  into  the  soil.  Plowing 
should  follow  as  closely  as  possible  the  spreading  of  the 
manure,  except  when  it  is  intended  for  a  top  dressing. 

293.  Place  of  farm  manure  in  crop  rotation.  —  When  a 
crop  rotation  includes  grass  or  clover  as  one  of  the  courses, 
the  application  of  farm  manure  may  well  be  made  at  that 
time  as  a  dressing.  It  can  thus  be  spread  at  times  when 
cultivated  land  would  not  be  accessible,  and  the  crop  of  hay 


232 


SOILS   AND   FERTILIZERS 


will  profit  greatly.  Sod,  when  plowed  under,  is  frequently 
planted  to  corn  —  a  crop  that  is  rarely  injured  by  farm  ma- 
nure. Experiments  in  Illinois  indicate  the  great  response 
of  clover  to  farm  manure,  as  compared  with  oats  and  corn. 

Table  54.  —  Increased  Crop  Yields  and  Values  When  Manure 
Was  Applied  to  Corn  and  Oats  and  to  Clover 


Percentage  Increase 
in  Yield 

Percentage  Value 
of  Increase 

Treatment 

Corn  and 
Oats 

Clover 

Corn  and 

Oats 

Clover 

Manure 

Manure,  lime  and  phosphate 

11 

30 

92 
141 

$  7.53 
12.21 

$10.08 
15.48 

QUESTIONS 

1.  What  plant  nutrients  does  farm  manure  contain,  and  what 
indirect  fertilizing  material  ? 

2.  In  what  ways  is  the  organic  matter  of  farm  manure  beneficial 
to  soils  ? 

3.  Which    is    richer  in    plant-food  materials,   liquid  or  solid 
manure  ? 

4.  What  constituent  should  farm  manure  have  added  to  it  in 
order  that  it  should  be  a  well-balanced  fertilizer  ? 

5.  What  farm  animal  produces  the  largest  quantity  of  manure 
for  every  1000  pounds  of  live  weight  ? 

6.  Which  produces  the  more  valuable  manure,  a  ration  rich 
in  plant-food  materials,  or  one  poor  in  these  substances  ? 

7.  Which  of  the  farm  animals  furnishes  a  manure  having  the 
greatest  commercial  value  a  ton  ? , 

8.  In  what  two  ways  does  farm  manure  suffer  loss  on  standing  ? 

9.  How  is  nitrogen  likely  to  be  lost  by  fermentation,  and  what 
condition  is  likely  to  bring  this  about  ? 

10.  What  substances  are  lost  by  the  leaching  of  manure  ? 
What  materials  are  used  for  conserving  manure  ? 
Is  it  better  to  store  manure,  or  to  haul  it  directly  to  the  land  ? 


11. 

12. 

Why? 

13. 


Discuss  the  place  of  manure  in  the  crop  rotation. 


FARM    MANURES  233 


LABORATORY    EXERCISES 

Exercise  I.  —  Study  of  farm  manure. 

In  one  or  more  trips  through  the  community  the  class  may  study 
in  a  practical  way  the  following  points  regarding  farm  manure  and 
its  utilization. 

1.  Enter  a  horse  stable  where  fresh  manure  is  lying  in  the  stalls. 
Observe  the  odor  of  ammonia.  Explain  the  reason  for  such  an  odor 
and  its  significance. 

2.  Compare  horse  manure  and  cattle  manure  as  to  weight,  struc- 
tural condition  and  amount  of  water.  What  relation  may  these 
characteristics  have  to  fermentation  and  to  the  handling  of  the 
manures  ? 

3.  In  the  same  way  compare  swine,  sheep  and  poultry  manures. 

4.  Examine  the  teachings  from  an  exposed  manure  pile.  What 
is  the  color  of  such  liquid  and  what  plant-food  materials  does  it  prob- 
ably contain  ? 

5.  Study  the  various  ways  of  handling  manure  that  are  in  vogue 
in  the  community.  List  and  discuss  their  good  and  poor  points, 
remembering  that  the  method  that  would  entail  the  least  loss  of 
plant-food  material  may  not  always  be  practicable,  due  to  lack  of 
capital  or  to  the  press  of  the  season's  work.  The  common  ways 
of  handling  manure  are  :  hauling  directly  to  the  field  and  either 
(1)  spreading  or  (2)  leaving  in  piles  for  later  distribution,  (3)  stor- 
ing in  a  covered  barnyard,  (4)  storing  in  a  manure  pit,  (5)  allowing 
manure  to  be  tramped  down  behind  the  animals  or  (6)  storing  in 
piles  either  under  cover  or  exposed. 

6.  Study  the  mechanism  and  operation  of  a  manure-spreader. 
An  efficient  spreader  should  run  easily  and  yet  distribute  the  manure 
evenly  and  in  a  finely  divided  condition. 

Exercise  II.  —  Experiments  with  farm  manure. 

Plat  experiments  similar  to  those  suggested  in  Exercise  IV,  Chap- 
ter XVI  might  be  carried  out  with  profit  with  farm  manure.  The 
effect  of  different  amounts  of  manure,  the  relative  returns  of  manure 
from  different  classes  of  animals,  the  influence  of  lime  on  the  return 
from  the  application  of  manure,  and  the  residual  influence  of  manure 
are  only  a  few  of  the  possible  tests  that  might  be  made. 

Tests  as  described  in  Exercise  III,  Chapter  XI  might  be  carried 
out  with  manure  as  well  as  with  commercial  fertilizers  and  lime  if 
plats  of  soil  are  not  available. 


234  SOILS    AND    FERTILIZERS 

Exercise  III.  —  The  value  of  manure  on  the  home-farm. 

From  the  data  in  the  text,  have  each  student  calculate  the 
probable  quantity  of  manure  produced  on  his  home-farm.  Have 
him  calculate  the  commercial  value  of  this  manure.  Then  from  the 
way  in  which  the  manure  is  handled  have  him  estimate  the  loss 
which  occurs  to  this  manure.  Now  discuss  the  probable  agricultural 
value  of  the  manure  as  compared  with  its  original  commercial  value. 

Exercise  IV.  —  Reinforcement  of  farm  manure. 

In  cooperation  with  some  near-by  farmer,  reinforce  some  farm 
manure,  allowing  the  pupils  to  aid  not  only  in  the  actual  work,  but 
in  the  determination  of  the  kind  and  amount  of  reinforcing  materials 
to  use.  Calculate  from  the  quantities  used  and  their  composition 
as  given  in  the  text,  the  probable  composition  of  the  manure  after 
the  treatment  and  determine  whether  it  has  become  a  properly 
balanced  material.  The  reinforced  manure  should  be  spread  in 
the  field  so  that  its  influence  on  the  succeeding  crop  may  be  com- 
pared with  untreated  manure.  Reinforcements  with  different  ma- 
terials may  even  be  compared  under  actual  field  conditions. 

Exercise  V.  —  Building  of  a  compost  pile. 

Farm  manure  in  a  compost  pile  supplies  the  organisms  which 
bring  about  the  decay  of  the  sod,  leaves  or  other  plant  materials 
which  are  to  be  reduced  to  simple  compounds.  Composted  mate- 
rials are  of  especial  value  in  greenhouses  and  gardens  in  supplying 
organic  matter  to  the  soil,  that  a  good  structure  may  be  maintained. 

Choose  a  level  spot  on  which  to  locate  the  compost  pile.  First 
put  down  a  layer  of  sod,  moistening  if  necessary  until  optimum  con- 
ditions are  attained.  Next  apply  a  thin  layer  of  fine,  well-rotted 
manure,  then  sod  and  so  on  till  the  pile  is  complete.  The  pile  may 
be  as  large  as  necessary  or  convenient  and  should  be  level  on  top  to 
prevent  the  rainfall  from  running  off  the  surface.  If  the  interior  of 
the  pile  is  moist  to  begin  with,  it  will  stay  moist  through  the  period 
given  to  fermentation.  Six  months  or  a  year  are  necessary  for 
effective  composting. 

Other  materials  than  sod  may  be  placed  in  a  compost  heap, 
such  as  leaves,  vines  of  all  kinds,  rotted  vegetables,  garbage,  small 
sticks,  etc.  It  is  a  good  practice  also  to  add  lime  to  the  pile  to  keep 
it  sweet.  If  the  material  is  to  be  used  as  a  fertilizer  as  well  as  to 
condition  the  soil,  acid  phosphate  may  also  be  added. 


CHAPTER  XVIII 
GREEN-MANURES 

Crops  that  are  grown  primarily  for  the  purpose  of  being 
plowed  under  to  improve  the  soil  are  called  green-manures. 
They  may  benefit  the  soil  in  one  or  more  of  four  ways  :  (1)  By 
utilizing  soluble  plant-food  material  that  would  otherwise 
leach  from  the  soil ;  (2)  by  incorporating  vegetable  matter 
with  the  soil ;  (3)  leguminous  crops,  when  used,  add  to  the 
available  nitrogen  of  the  soil ;  (4)  plant-food  materials  from 
the  lower  soil  may  be  brought  tfcrthe  surface  soil. 

A  large  number  of  crops  may  be  used  for  this  purpose, 
while  the  climate  determines  to  some  extent  which  crops 
should  be  used.  Crops  that  can  be  planted  in  the  fall  to 
grow  during  the  cool  weather  may  be  utilized  when  otherwise 
the  land  would  frequently  lie  bare.  Leguminous  crops  have 
the  great  advantage  of  acquiring  nitrogen  from  the  air.  Deep- 
rooted  crops  usually  accumulate  a  large  amount  of  nutriment 
from  the  soil  and  considerable  from  the  lower  depths.  They 
are  therefore  useful  in  bringing  plant-food  material  to  the 
upper  layers  of  soil.  Succulent  crops  decompose  easily,  and 
dry  out  the  soil  less,  when  plowed  under,  than  do  woody  crops. 
Crops  with  extensive  root- systems  prevent  loss  of  soluble 
matter  more  thoroughly  than  do  plants  with  small  root 
systems. 

294.  Protective  action  of  green-manures.  —  It  has  been 
shown  in  section  121  that  the  growth  of  crops  on  land  may 
prevent  a  large  loss  of  plant-food  material,  especially  nitrogen 

235 


236 


SOILS    AND    FERTILIZERS 


and  lime,  in  drainage  water.  If,  therefore,  green-manure  crops 
cover  the  soil,  when  otherwise  nothing  would  be  growing  on  it, 
they  exercise  a  protective  action.  In  the  case  of  orchards  a 
green-manure  crop  saves  much  nutriment  as  compared  with 
clean  cultivation.  A  catch-crop,  like  rye,  that  is  sown  in  the 
fall  after  a  summer  crop  has  been  harvested  and  is  plowed 
under  in  the  spring,  saves  some  plant-food  material. 

295.  Materials  supplied  by  green-manures.  —  Probably 
the  most  beneficial  effect  exerted  by  green-manures  is  the  ad- 
dition of  organic  matter  to  soil.  Practically  the  only  source 
of  organic  matter  is  in  the  form  of  farm  manure  or  of  plant 
residues.  Farm  manure  is  yearly  becoming  more  scarce 
and  expensive.  Some  substitute  must  be  found.  In  an 
average  crop  of  green-manure,  from  five  to  ten  tons  of 
material  is  turned  under.  Of  this,  from  one  to  two  tons  is 
dry  matter,  and  from  four  to  eight  tons  is  water.  This  would 
correspond  to  a  dressing  of  four  to  eight  tons  of  farm  manure, 
so  far  as  the  organic  matter  alone  is  concerned. 

Legumes  add  nitrogen  as  well  as  organic  matter.  The 
nitrogen  contained  in  a  ton  of  the  green  crop,  when  in  a  con- 
dition to  plow  under,  is  as  follows  : 


Table   55.  —  Quantities    of   Nitrogen   in   Some    Leguminous 
Green-Manure  Crops 


Crop 


Red  or  mammoth  clover 
Crimson  clover   . 
Alsike  clover  .... 

Alfalfa 

Cowpeas 

Soy  beans 

Canada  field  peas    .     . 


Nitrogen 
per  Ton, 
Pounds 

Probable 
Yield  per 
Acre,  Tons 

10 

6 

9 

6 

10 

5 

14 

8 

8 

6 

10 

6 

11 

5 

Nitrogen 

per  Acre, 

Pounds 


60 

54 

50 
112 
48 
60 
55 


GREEN-MANURES 


237 


Not  all  of  the  nitrogen  contained  in  these  crops  is  taken 
from  the  air.  On  soils  rich  in  nitrogen,  a  considerable  pro- 
portion may  be  obtained  from  the  soil.  On  poor  soils,  the 
proportion  derived  from  the  atmosphere  is  considerably 
larger.  Soils  needing  nitrogen  most  are  those  that  benefit 
most  largely  from  its  application. 

296.  Transfer  of  plant-food  materials.  —  There  is  a  trans- 
fer of  plant  nutrients  in  a  double  sense  :  (1)  removal  of  these 


L055  LAR6ELY  ORGANIC  * 
WITH  SOME  NITROGEN 
AND  PHOSPHORIC  ACID 


ANIMAL 


TO  MARKET 


LARGE  L055  OF  0R6ANIC  * 
MATTER,  NITROGEN,  PHOS- 
PHORIC ACID  AND  POTASH 


GREEN  MANURE 


Fig.  34.  —  Movements  of  plant-food  materials.  After  absorption  by  the 
plant  they  may  be  returned  in  whole  or  in  part  to  the  soil.  If  grain  and 
straw  or  hay  are  sold  nothing  but  the  stubble  and  roots  are  returned.  If 
fed  to  animals,  part  may  be  returned  in  the  manure.  If  plowed  under  as 
green-manure,  all  are  returned. 

substances  from  combination  with  other  minerals  and  their 
conversion  into  combinations  with  organic  matter;  (2)  re- 
moval from  lower  soil  by  absorption  by  roots  and  the  deposi- 
tion of  this  material  in  the  upper  layer  of  soil  when  the  plant 
dies  and  is  plowed  under.  The  first  of  these  transfers  results 
in  an  improved  condition  of  the  plant  nutrients,  because  in 
the  combinations  with  organic  matter  they  are  in  general 
more  available  to  plants  than  when  in  combinations  with 


238 


SOILS    AND    FERTILIZERS 


inorganic  matter.  By  the  second  form  of  transfer  the  nutri- 
ents  in  this  available  form  are  deposited  in  the  upper  soil  from 
which  most  crops  draw  the  larger  part  of  their  nutriment. 

297.  Crops  used  for  green-manuring.  —  The  following  table 
contains  a  list  of  the  plants  commonly  used  as  green-manures 
both  in  cultivated  fields  and  in  orchards,  together  with  some 
information  as  to  the  season  of  the  year  when  they  may  be 
used  and  whether  adapted  to  northern  or  southern  conditions. 

Table  56.     Crops  Used  as  Green-Manures 


Legumes  (annual) 

Canada  field  pea 

Hairy  vetch 

Crimson  clover 

Peanut        

Velvet  bean 

Soy  bean    

Cowpeas 

Legumes  (biennial  or  perennial) 
Red  or  mammoth  clover   .     .     . 

Alsike  clover 

Alfalfa 

Sweet  clover 

Non-Legumes 

Rye 

Oats 

Buckwheat 

Cowhorn  turnips 

Mustard 

Rape 


Season 


summer 

winter 

winter 

summer 

summer 

summer 

summer 

one  year  at  least 
one  year  at  least 
one  year  at  least 
one  year  at  least 

winter 

fall  or  early  spring 

fall  and  summer 

summer 

summer 

summer  and  fall 


Region 


Northern  states 
Northern  and  southern  states 
Middle  and  southern  states 
Middle  and  southern  states 
Middle  and  southern  states 
Middle  and  southern  state3 
Southern  states 

Northern  states 

Northern  states 

Northern  and  southern  states 

Northern  and  southern  states 

Northern  and  middle  states 
Northern  and  middle  states 
Northern  states 
Northern  states 
Northern  states 
Northern  states 


A  soil  that  has  become  less  productive  under  cultivation, 
and  that  must  be  improved  before  profitable  crops  can  be 
grown,  receives  more  benefit  from  the  use  of  legumes  than 
from  any  other  crop.  The  legume  to  use  is  naturally  the  one 
best  adapted  to  the  region  in  which  the  soil  is  located. 

The  perennial  or  biennial  legumes  are  too  slow  of  growth 
really  to  be  considered  green-manure  crops.     They  are  like 


Plate  XVI.  Soil  Covers.  —  Cover-crops  may  consist  merely  of 
weeds  allowed  to  grow  voluntarily,  as  shown  in  the  upper  figure,  or  of 
grain  or  other  planted  crops,  as  shown  in  the  lower. 


GREEN-MANURES  239 

timothy  and  other  grasses  and  can  well  be  grown  for  hay,  only 
the  sod  being  plowed  under.  Only  in  the  case  of  very  much 
run  down  soils  are  these  crops  plowed  under.  Crimson 
clover  is  an  annual,  and  in  the  central  and  southern  states 
may  be  sown  in  the  fall  and  plowed  under  in  the  late  spring, 
thus  making  use  of  a  period  of  the  year  when  the  ground  is 
least  likely  to  be  occupied  by  a  crop.  Cowpeas,  soy  beans 
and  field  peas  must  be  raised  during  the  summer  months. 
Vetch  promises  to  be  a  satisfactory  green-manure  for  winter 
use  in  the  northern  states,  when  the  cost  of  seed  becomes 
less  than  it  is  at  present. 

Where  it  is  desired  to  keep  a  crop  on  the  soil  during  the 
autumn,  winter  and  spring,  for  the  purpose  of  utilizing  the 
soluble  plant-food  material,  the  cereals,  especially  rye,  are 
useful.  Buckwheat,  on  account  of  its  ability  to  grow  on  poor 
soil,  is  adapted  to  use  as  a  green-manure,  but  it  must  be 
grown  in  the  summer  or  early  fall. 

298.  When  green-manures  may  be  used.  —  The  most 
economical  way  to  use  green-manures  is  between  the  regular 
crops,  rather  than  to  lose  a  crop  for  the  purpose  of  applying 
green-manure.  Between  a  small  grain  crop  and  a  spring- 
planted  crop,  there  is  usually  opportunity  for  some  green- 
manure  to  be  raised,  even  in  the  northern  states.  This  crop 
may  be  rye,  vetch,  buckwheat  or  rape  and  in  the  southern 
states  may  be  added  crimson  clover,  which  is  perhaps  best 
for  that  region.  In  the  South,  however,  there  is  much 
more  opportunity  for  the  use  of  green-manure  crops  on  ac- 
count of  the  longer  season.  Where  timothy  and  red  clover 
grow  successfully,  it  is  probably  best  to  rely  on  the  sod  of 
these  crops  to  furnish  green-manure  rather  than  to  attempt 
any  system  that  would  necessitate  dropping  a  crop  from  the 
rotation.  By  a  judicious  fertilization  of  the  hay  crops,  a 
heavy  sod  may  be  produced,  thus  utilizing  the  inorganic 
matter  of  the  fertilizer  to  produce  organic  matter  in  the  sod. 


240  SOILS    AND    FERTILIZERS 

It  is  probably  where  special  crops  are  produced  that  green- 
manures  will  reach  their  greatest  usefulness.  Their  use  in 
orchards  is  well  established.  For  this  purpose  they  are 
plowed  under  in  the  spring  and  planted  in  midsummer. 
Potato-growers  and  even  market-gardeners  are  using  green- 
manures  in  increasing  quantity.  ^ 

299.  Handling  green-manure  crops.  —  The  stage  of  growth 
at  which  green-manures  should  be  plowed  under  has  a  rather 
important  bearing  on  their  effect  on  the  soil.  In  order  that 
they  shall  decompose  readily,  they  should  be  succulent  when 
incorporated  with  the  soil.  If  plants  that  have  fully  ripened 
are  plowed  under,  they  decompose  very  slowly  and  interfere 
with  the  formation  of  nitrates.  An  acid  soil  is  unfavorable 
to  the  decomposition  of  green-manures  and  to  the  formation 
of  nitrates ;  hence  it  is  desirable  that  lime  be  applied  before 
planting  the  manure  crops  unless  the  soil  is  already  well 
supplied  with  lime. 

QUESTIONS 

1.  Describe  what  is  meant  by  green-manure  crops. 

2.  State  four  ways  in  which  they  may  be  beneficial  to  the  soil. 

3.  What  two  substances  are  prevented  from  being  leached  from 
soil  in  large  quantities  by  the  growth  of  green-manure  crops  ? 

4.  How  do  legumes  differ  from  other  green-manures  in  con- 
tributing to  soil  fertility  ? 

5.  In  what  two  ways  is  there  a  transfer  of  plant  nutrients  brought 
about  by  the  use  of  green-manures,  and  how  do  they  benefit  the  soil  ? 

6.  Name  five  leguminous  green-manure  crops  and  state  the  time 
of  year  in  which  they  are  generally  planted  in  your  locality. 

7.  Give  the  same  information  regarding  five  non-legumes. 

8.  What  is  the  disadvantage  of  plowing  under  green-manure 
crops  when  they  are  fully  ripe  ? 

LABORATORY   EXERCISES 

Exercise  I.  —  Study  of  green-manure  in  the  field. 
Plan  a  field  trip  to  some  farm  where  a  crop  is  being  turned  under 
for  green-manure.     Determine  whether  the  time  is  most  favorable 


GREEN-MANURES  241 

for  the  operation.  Study  the  action  of  the  plow  which  is  being 
used  and  see  if  the  depth  of  the  plowing,  the  inclination  of  the 
furrow  slice,  and  the  covering  of  the  green  material  is  as  it 
should  be. 

Calculate  the  weight  of  the  crop  being  turned  under  and  with 
this  as  a  basis,  figure  the  pounds  of  water,  dry  matter,  nitrogen, 
phosphoric  acid  and  potash  being  placed  in  the  soil  per  acre.  If 
the  crop  is  a  legume,  make  a  guess  as  to  the  probable  gain  of  the  soil 
in  nitrogen.     Is  this  nitrogen  available  or  unavailable  ? 

Exercise  II.  —  Green-manure  and  the  rotation. 

Take  a  number  of  good  practical  rotations  and  indicate  where, 
in  the  succession  of  crops,  a  green-manure  might  be  introduced. 
Encourage  the  pupils  to  bring  data  from  their  home  farms  for  this 
study.  Tabulate  such  material  and  study  it  in  the  class  room. 
Also  bring  up  the  question  in  relation  to  gardening  and  trucking. 
Discuss  the  necessity,  advisability  and  ways  of  introducing  a  green- 
manure  under  such  conditions. 


CHAPTER  XIX 
CROP  ROTATION 

Early  in  the  development  of  agriculture,  it  was  understood 
that  a  succession  of  different  crops  on  any  piece  of  land 
gave  better  returns  than  did  one  crop  raised  continuously. 
The  practice  of  changing  the  crops  raised  each  year  thus 
became  customary,  and  the  prevalence  of  the  method  among 
European  peoples  shows  that  its  benefits  are  widely  appre- 
ciated. In  Great  Britain  and  some  of  the  countries  of 
Europe,  crop  rotations  have  been  most  systematically 
and  effectively  developed .  S  uch  development  has  been  stim- 
ulated by  the  diminishing  productiveness  of  the  soil,  con- 
sequent upon  long-continued  cultivation,  coupled  with  an 
increasing  and  progressive  population.  Regions  having 
undepleted  and  uninfested  soil,  as  was  formerly  the  case  in 
the  prairie  region  of  the  United  States,  and  countries  that 
have  an  unprogressive  people,  like  those  of  India,  have  done 
little  with  crop  rotation. 

Another  condition  that  discourages  the  use  of  crop  rotation 
is  the  suitability  of  a  region  to  the  production  of  some  one 
crop  of  outstanding  value,  combined,  perhaps,  with  a  rela- 
tively cheap  supply  of  fertilizing  material.  These  conditions 
obtain  in  the  cotton  belt  of  the  United  States.  The  abun- 
dant use  of  fertilizers  may  postpone  for  a  long  time  the 
recourse  to  crop  rotation. 

300.  Crop  rotation  and  soil  productiveness.  —  There 
are  many  benefits  to  be  derived  from  a  proper  rotation  of 

242 


CROP   ROTATION  243 

crops  that  are  not  directly  concerned  with  soil  productive- 
ness, and  of  these  this  book  does  not  treat.  In  a  number 
of  ways  crop  rotation  may  directly  affect  the  soil,  and  these 
will  be  discussed  under  several  different  heads. 

301.  Root  systems  of  different  crops.  —  Some  crops  have 
roots  that  penetrate  deeply  into  the  subsoil,  while  others  are 
only  moderately  deep-rooted  and  still  others  very  shallow- 
rooted.  Among  the  deeply  rooted  plants  are  alfalfa,  clover, 
certain  of  the  root  crops  and  some  of  the  native  prairie 
grasses.  Among  those  having  moderately  long  roots  are 
oats,  corn,  wheat  meadow  iescue  and  a  few  other  grasses, 
and  among  those  having  shallow  roots  are  barley,  turnips 
and  many  of  the  cultivated  grasses. 

As  plants  draw  their  nourishment  from  those  portions  of  the 
soil  into  which  their  roots  penetrate,  the  deeper  soil  is  not 
called  upon  to  provide  food  material  for  the  shallow-rooted 
crops,  and  the  deep-rooted  crops  remove  relatively  less  of 
their  nutrients  from  the  surface  soil.  It,  therefore,  happens 
that  a  rotation  involving  the  growth  of  deep  and  shallow- 
rooted  plants  effects,  by  utilizing  a  larger  area  of  the  soil, 
a  more  economical  utilization  of  plant  nutrients  than  would 
a  continuous  growth  of  either  kind. 

302.  Nutrients  removed  from  soil  by  different  crops.  — 
Some  crops  require  large  amounts  of  one  fertilizing  constit- 
uent, while  others  take  up  more  of  another.  For  instance, 
wheat  crops  are  able  to  utilize  the  potassium  and  phosphorus 
of  the  soil  to  a  considerable  degree,  but  have  less  ability  to 
secure  nitrogen.  They  are  usually  much  benefited  by  the 
application  of  a  nitrate  fertilizer  and  leave  in  the  soil  a  con- 
siderable residue  of  nitrogen  that  may  be  available  to  other 
plants.  A  number  of  other  crops,  as,  for  example,  beets  and 
carrots,  can  utilize  this  residual  nitrogen. 

Grasses  remove  comparatively  little  phosphoric  acid. 
Potatoes  remove  very  large  quantities  of  potash.     A  rota- 


244  SOILS    AND    FERTILIZERS 

tion  of  crops  is,  therefore,  less  likely  to  cause  a  deficiency 
of  some  one  constituent  than  is  a  continuous  growth  of 
one  crop,  and  it  utilizes  more  completely  the  available 
nutrients. 

303.  Some  crops  or  crop  treatments  prepare  nutriment 
for  other  crops.  —  It  is  quite  evident  that  leguminous  crops 
not  only  leave  in  the  soil  an  accumulation  of  organic  nitrogen 
transformed  by  bacteria  from  atmospheric  nitrogen,  but  that 
they  leave  part  of  the  nitrogen  in  a  form  readily  available 
for  use  by  other  plants.  The  presence  of  a  grass  crop  on  the 
land  for  several  years  favors  the  action  of  non-symbiotic 
nitrogen-fixing  bacteria.  The  grass  crops  also  leave  a  very 
considerable  amount  of  organic  matter  in  the  soil,  which 
by  its  gradual  decomposition  contributes  both  directly  and 
indirectly  to  the  supply  of  available  nutrients. 

Stirring  the  soil  at  intervals  during  the  summer  greatly 
facilitates  decomposition,  and  leaves  a  supply  of  easily  avail- 
able food  material.  The  introduction  of  intertilled  crops  in 
the  rotation  thus  serves  to  prepare  nutriment  for  those  that 
receive  no  intertillage. 

304.  Crops  differ  in  their  effect  on  soil  structure.  —  Plants 
must  be  included  among  the  factors  that  affect  the  arrangement 
of  soil  particles.  The  result  of  root  growth  is  usually  to  im- 
prove the  physical  condition  of  soil.  In  general,  crops  with 
rather  shallow  and  very  fibrous  roots  are  most  beneficial,  at 
least  to  the  surface  soil.  Millet,  buckwheat,  barley  and  to  a 
less  extent,  wheat  leave  the  soil  in  a  friable  condition.  It  is  on 
heavy  soils  that  this  property  is  most  beneficially  exercised. 
Tap-rooted  plants,  and  others  with  few  surface  roots,  do  not 
exhibit  this  action.  Alfalfa  and  some  root  crops  are  likely 
to  leave  the  soil  rather  compact  as  compared  with  the  crops 
mentioned  above.  The  effect  of  sod  is  nearly  always  bene- 
ficial to  heavy  soils,  and  this  is  one  of  the  reasons  for  using 
a  grass  crop  in  a  rotation. 


CROP   ROTATION  245 

305.  Certain  crops  check  certain  weeds.  —  By  rotating 
crops  the  weeds  that  nourish  during  the  presence  of  one  crop 
on  the  land  may  be  greatly  checked  by  succeeding  crops. 
Some  weeds  are  best  destroyed  by  smothering,  for  which 
purpose  small  grain,  and  notably  corn  or  sorghum  grown  for 
fodder  are  effective.  Other  weeds  are  most  injured  by  til- 
lage, to  accomplish  which  the  hoed  crops  are  needed ;  while 
others  can  best  be  checked  by  the  presence  of  a  thick  sod  on 
the  ground  for  a  number  of  years.  In  the  warfare  against 
weeds  that  must  be  waged  wherever  crops  are  raised,  the  use 
of  different  crops  involving  different  methods  of  soil  treat- 
ment is  of  great  service. 

306.  Plant  diseases  and  insects.  —  Many  plant  diseases 
and  many  insects  spend  their  resting  stages  and  larval  exist- 
ence in  the  soil.  A  continuous  growth  of  any  one  crop  on  the 
soil  favors  the  increase  of  these  species  by  providing  each 
year  the  particular  plant  on  which  they  thrive.  A  change  of 
crops,  by  removing  the  host  plants,  causes  the  disappearance 
of  many  diseases  and  insects  through  their  inability  to  reach 
their  host  plants.  A  long  rotation,  such  as  is  frequently 
used  in  Great  Britain,  is  particularly  effective  in  eradicating 
those  diseases  that  persist  in  the  soil  for  a  number  of  years. 

In  the  case  of  diseases  that  affect  more  than  one  species 
of  plant,  as  does  the  beet  and  potato  scab,  there  is  need  for 
special  care  in  arranging  the  rotation.  Such  considerations 
may  make  it  desirable  to  change  the  plan  of  a  rotation. 
Another  feature  of  the  relation  of  crop-rotation  to  plant  dis- 
eases is  that  the  more  thrifty  growth  obtainable  under  rota- 
tion assists  the  crop  to  withstand  many  diseases. 

307.  Loss  of  plant-food  material  between  plantings. — Many 
systems  of  crop  rotation  permit  a  more  constant  use  of  the 
land  than  is  possible  with  continuous  growth  of  most  annual 
crops.  As  a  soil  bearing  no  crop  on  it  always  loses  more 
plant-food  material  in  the  drainage  water  than  does  one  on 


246  SOILS    AND    FERTILIZERS 

which  plants  grow,  it  is  thus  possible,  by  a  well-chosen 
rotation,  to  save  plant-food  material  that  would  otherwise 
be  lost. 

308.  Production  of  toxic  substances  from  plants.  —  Tl^at 
soil  sometimes  contains  organic  substances  that  exert  an 
injurious  effect  on  the  growth  of  certain  plants  is  indicated  by- 
recent  experiments  and  was  surmised  by  some  early  writers 
on  the  subject.  De  Candolle  was  probably  the  first  to  ad- 
vance the  idea  in  1832.  He  suggested  that  at  least  some 
plants  excrete  from  their  roots  substances  that  are  injurious 
to  the  growth  of  the  plants  themselves  and  others  of  their 
species,  although  the  excreta  may  be  harmless  or  even  bene- 
ficial to  other  plants.  This  he  considered  one  of  the  reasons 
for  the  failure  of  many  crops  to  succeed  when  grown  contin- 
uously, while  the  same  soil  may  be  productive  under  a  rota- 
tion of  crops. 

Of  recent  years  this  subject  has  been  investigated  exten- 
sively in  the  United  States  and  to  some  extent  in  Europe. 
There  appears  to  be  no  doubt  that  toxic  substances  of  an 
organic  nature  sometimes  occur  in  soils,  and  there  is  evi- 
dence that  some  of  them  are  connected  with  the  growth  of 
certain  crops  to  which  they  are  injurious.  In  most  soils 
containing  toxic  substances  the  injurious  effect  is  exerted  on  a 
large  number  of  plants  rather  than  only  on  those  that  have 
been  previously  grown.  It  is  still  a  question  to  what  extent 
excretion  from  roots  or  partial  decomposition  of  plant  residues 
are  responsible  for  the  poor  growth  that  results  from  the 
continuous  growth  of  crops  on  the  same  soil. 

309.  Management  of  a  crop  rotation.  —  The  advantages 
of  a  crop  rotation  are  so  apparent  and  are  connected  so  closely 
with  the  profits  to  be  derived  from  farming  that  there  can  be 
no  doubt  regarding  the  advisability  of  practicing  a  rotation, 
even  when  some  one  crop  may  be  much  more  profitable  than 
any  others  that  can  be  grown.     Thus  even  in  regions  and  on 


CROP   ROTATION  247 

soil  particularly  favorable  to  the  production  of  any  one  crop, 
like  tobacco,  cotton,  hay,  corn  or  wheat,  it  will  seldom  be  ad- 
visable to  raise  one  crop  to  the  exclusion  of  others,  but  the 
most  rational  practice  will  generally  provide  for  some  system 
of  crop  rotation. 

There  are  three  classes  of  crops  that  should,  so  far  as  possi- 
ble, have  a  place  in  any  rotation.  These  are  legumes,  sod 
crops  or  grasses  and  intertilled  crops.  The  value  of  legumes 
as  nitrogen  gatherers  has  already  been  discussed.  It  is  partic- ' 
ularly  on  poor  land  that  legumes  are  of  most  benefit,  and  if 
some  of  the  tops,  as  for  instance,  the  second  growth  of  clover, 
be  plowed  under,  their  value  will  be  greater. 

Sod  crops  are  of  great  value  in  furnishing  organic  matter 
to  the  soil.  The  larger  the  hay  crop,  the  more  sod  produced, 
which  is  a  double  incentive  to  the  use  of  fertilizers  and 
farm  manure  on  this  crop  (see  §  204).  Sod  also  forms 
a  favorable  condition  for  the  fixation  of  nitrogen.  Legumes 
appear  to  have  one  advantage  over  sod  crops  as  nitrogen 
gatherers,  in  that  the  nitrogenous  matter  remaining  in  the  soil 
is  more  available  to  some  crops,  at  least,  and  is  more  readily 
converted  into  nitrates. 

In  each  course  of  a  rotation  there  should  be,  if  possible,  one 
intertilled  crop,  like  corn,  cotton,  potatoes  or  cabbage.  The 
intertilled  crop  should  follow  the  sod  crop,  or  the  legume, 
because  the  cultivation  given  the  soil  throughout  the  summer 
produces  a  condition  favorable  to  the  decomposition  of  the 
organic  matter  furnished  by  the  sod.  Except  where  the  con- 
servation of  moisture  is  an  important  factor,  the  use  of  an 
intertilled  crop  is  preferable  to  a  clean  fallow,  as  it  is  more 
economical  of  the  nitrogen  and  lime  supply,  and  appears  to 
result  in  better  crops  the  year  following. 

Other  crops  to  be  used  in  the  rotation  will  be  determined  by 
the  climate,  soil,  market  and  convenience  in  handling. 

Fertilization  of  the  rotation  is  discussed  in  section  271. 


248  SOILS    AND    FERTILIZERS 

QUESTIONS 

1.  What  advantage  is  gained  by  alternating  deep-rooted  with 
shallow-rooted  plants  in  a  rotation  ? 

2.  Why  is  a  rotation  of  crops  less  likely  to  cause  a  deficiency  in 
some  one  constituent  of  the  soil  than  is  the  continuous  growt^L  of 
one  crop  ? 

3.  In  what  ways  do  some  crops  and  some  crop  treatments  pre- 
pare available  nutriment  for  other  crops  ? 

4.  How  may  soil  structure  be  affected  by  crop  rotation  ? 

5.  Explain  the  relation  of  crop  rotation  to  weeds. 

6.  Explain  the  relation  of  crop  rotation  to  plant  diseases  and 
insects. 

7.  How  may  plant  nutrients  be  prevented  from  leaching  by  the 
use  of  the  proper  rotation  ? 

8.  What  three  classes  of  crops  should  have  a  place  in  any  rota- 
tion and  why  ? 

LABORATORY   EXERCISES 

Exercise  I.  —  Crop  rotations. 

Study  standard  crop  rotations  from  different  parts  of  the  United 
States  as  to  crops  grown,  climate,  markets,  fertility  of  the  soil, 
fertilization,  etc.  Try  to  find  the  reason  for  the  use  of  each  rotation 
under  its  particular  conditions.  , 

With  the  aid  of  the  pupils,  obtain  a  number  of  the  rotations  used 
in  the  community  or  county.  Study  these  from  all  standpoints, 
and,  if  possible,  suggest  improvements.  A  rotation  survey  of  the 
community  might  be  made  in  order  that  data  valuable  to  the 
farmers,  as  well  as  to  the  pupils,  shall  be  obtained.  The  students 
should  aid  in  this  as  well  as  in  the  tabulation  and  interpretation  of 
the  data. 

Exercise  II.  —  Fertilizing  the  rotation. 

Under  given  conditions  have  the  pupil  work  out  the  fertilization 
of  a  standard  rotation  for  the  locality.  This  means  not  only  the 
kinds  and  quantities  of  fertilizer  to  apply,  at  what  point  in  the 
rotation  to  add  them  and  at  what  time  of  year  to  put  on  the  soil, 
but  also  the  use  of  lime,  green  manure  and  farm  manure.  Such  a 
study  should  be  a  summation  of  many  of  the  practices  and  principles 
of  good  soil  management. 


INDEX 


Absolute    specific    gravity,    of    soil    Air  of  soil,  oxygen  in,  146 


particles,  35. 

and  "heavy"  soil,  35. 

and  "light"  soil,  35. 
Absorbed  fertilizers,  100. 
Absorption,  of  lime  by  soils,  188. 

of  gases,  test  for,  111. 

selective,  99. 

selective,  test  for,  111. 
Absorptive  power  of  different  crops, 

107. 
Absorptive  properties  of  soils,  99. 
Acid  phosphate,  absorption  by  soil, 
173. 

manufacture  and  composition,  172. 

vs.  rock  phosphate,  174. 
Acid  soils,  described,  112. 

causes  of,  113. 

crops  adapted  to,  116. 

crops  injured  by,  116. 

effect  of  drainage  on,  113. 

effect  of  fertilizers  on,  114. 

effect  of  green  manures  on,  115. 

effect  of  plant  growth  on,  114. 

litmus  paper  test  for,  117. 

relation  to  bacteria,  129. 

tests  for,  122,  123. 

Truog  test,  118. 

weeds  that  nourish  on,  115. 
Adobe,  composition  of,  27. 

distribution  of,  27. 
iSColian  soils,  described,  26. 

adobe,  27. 

loess,  27. 
Air  of  soil,  composition,  145. 

control  of  movement,  148. 

control  of  volume,  148. 

demonstration  of  movement,  152. 

in  relation  to  drainage,  79. 

movements,  144. 

nitrogen  in,  147. 


quantities  present,  143. 

relation  to  pore  space,  143. 

relation  to  water,  144. 

usefulness  of,  146. 
Alkali  and  irrigation,  120. 

control  of,  121. 

effect  of  crops  on,  119. 

movements  of,  118. 

removal  of,  120. 

tolerance  of    different    plants    to, 
119. 
Alkali  soils,  nature  of,  118. 
Alluvial  soils,  character  of,  23. 

described,  22. 

distribution  of,  23. 

formation  of,  22. 
Ammonia,  absorption  by  plants,  156. 

test  for,  in  soil,  141. 
Ammonification,  132. 
Animals,  effect  on  structure,  41. 
Apatite,  plant-food  materials  in,  7. 
Apparent      specific      gravity,      and 
"heavy"  soil,  38. 

and  "light"  soil,  38. 

of  soil  particles,  38. 
Auger  for  sampling  soil,  29. 
Available  plant-food  materials,  94. 
Availability,      conditions     that      in- 
fluence, 95. 

of  nitrogenous  fertilizers,  166. 

Bacteria,  action  on  mineral  matter, 

129. 
ammonification  caused  by,  132. 
conditions  affecting  growth,  128. 
decomposition       of        nitrogenous 

organic  matter,  131. 
decomposition  of    non-nitrogenous 

organic  matter,  130. 
examination  of  nodules  for,  142. 


249 


250 


INDEX 


Bacteria,  in  relation  to  air  supply,  128. 

in  relation  to  lime,  189. 

in  relation  to  moisture,  128. 

in  relation  to  organic  matter,  129. 

in  relation  to  soil  acidity,  129. 

in  relation  to  soil  fertility,  129. 

in  relation  to  temperature,  129. 

nitrification  caused  by,  132. 

numbers  in  soils,  127. 
Basic  slag,  172. 

Calcite,  plant-food  material  in,  7. 
Capillary  capacity,  test  for,  87. 
Capillary  movement,  test  for,  86. 
Capillary  water,  63. 
Carbon  dioxide,  conditions  that  affect 
quantity,  146. 

demonstration  of  formation  in  soil, 
154. 

demonstration  of  presence  in  soil, 
153. 

functions  in  soil,  147. 

percentage    in    bare    and    planted 
soil,  106. 

percentage  in  soil  air,  145. 

production  by  microorganisms,  107. 

production  in  soils,  145. 
Chemical  analysis  of  soil,  98. 
Chemical    composition,    of    various 
soils,  91. 

relation  to  productiveness,  93. 
Class,  the  soil,  defined,  33. 

in  soil  survey,  44. 

method  for  determination,  34. 
Classification  of  soils  in  survey,  43. 
Colluvial  soils,  described,  22. 

formation  of,  22. 
Compaction    of    soil    due    to    root 

growth,  2. 
Compost,  building  of  a  pile,  234. 
Crop  rotation,  242. 
Crops,  relation  to  soil  texture,  32. 
Cumulose  soils,  composition  of,  21. 

described,  20. 

formation  of,  20. 
Cyanamid,  changes  in  the  soil,  162. 

composition  of,  161. 

manufacture  of,  161. 

Denitrification,  135. 

Dolomite,  plant-food  materials  in,  7. 


Drainage,    and    length    of    growing 
season,  80. 

and  available  water,  79. 

benefits  from,  78. 

by  open  ditches,  80.       * 

defined,  78. 

in  relation  to  soil  air,  79. 

in  relation  to  tilth,  79. 
Drainage     water,      composition     of, 

103,   104. 
Drains,  arrangement  of,  82. 

concrete,  81. 

tile,  81. 

Evaporation,  prevention  of,  74-77. 
proportion  of  rainfall  lost  by,  73. 

Feldspars,  plant-food  materials  in,  7. 
Fertility  of  soil  in  relation  to  bac- 
teria, 129. 
Fertilizer  constituents,  trade  values, 
200. 

experiments,  plan  for,  212. 

formulas  for  different  crops,  210. 

ingredients,  how  to  mix,  205. 

mixture,  calculation  of,  204. 
Fertilizers,  brands  of,  196. 

computation    of    wholesale    value, 
202. 

conditions  that  influence  effect  of, 
217. 

consumption  of,  in  U.  S.,  196. 

cumulative  need  of,  218. 

effect  on  soil  acidity,  114. 

for  different  crops,  207. 

for  different  soils,  211. 

for  grasses,  208. 

for  leguminous  crops,  208. 

for  orchards,  209. 

for  root  crops,  209. 

for  small  grains,  207. 

for  vegetables,  209. 

high  and  low  grade,  198, 

home  mixing  of,  203. 

inspection  and  control,  199. 

law  of  diminishing  returns,  215. 

methods  of  applying,  214. 

nitrogenous,  155. 

nitrogenous,  forms  of  nitrogen  in, 
157. 

phosphoric  acid,  171. 


INDEX 


251 


Fertilizers,  phosphoric  acid,  tests  for, 
177. 
potash,  179. 
potash,  tests  for,  185. 
response  of  soil  to,  218. 
tests  for  nitrogenous  fertilizers,  169. 
that  should  not  be  mixed,  203. 
the  limiting  factor,  215. 
the  purchase  and  mixing  of,  196. 
use  of,  207. 
Fertilizing  the  rotation,  213. 
Formation  of  soil,  agencies  concerned, 

11. 
Formations  of  soil,  18. 
Freezing  and  thawing  of  soil,  effect 

on  structure,  40. 
Frost,  effect  on  rock  disintegration, 
12. 

Gases,  diffusion  of,  144. 

effect  on  rock  disintegration,  14. 
Germs,  injurious  to  crops,  125. 

in  soil,  kinds  of,  125. 

not  directly  injurious  to  crops,  126. 
Glacial  soils,  composition  of,  26. 

described,  25. 

distribution  of,  26. 

formation  of,  25. 
Glaciers,    effect  on  rock  disintegra- 
tion, 13. 
Grains,  fertilizers  for,  207. 
Granite,  losses  during  soil  formation, 

15. 
Grasses,  fertilizers  for,  208. 
Gravitational  water,  67. 
Green  manures,  crops  used  for,  238. 

effect  on  soil  acidity,  115. 

handling,  240. 

materials  supplied  by,  236. 

nature  of,  235. 

protective  action  of,  235. 

when  to  use,  235. 
Guano,  165. 
Gypsum,  plant-food  material  in,  7. 

use  on  land,  192. 

Heat  and  cold,  effect  on  rock  disin- 
tegration, 12. 

Heat  of  soil,  sources  of,  149. 

"Heavy"  soil,  and  absolute  specific 
gravity,  35. 


"Heavy"  soil,  and  apparent  specific 

gravity,  38. 
Hematite,  plant-food  material  in,  7. 
Hygroscopic  water,  61. 

Ice,  effect  on  rock  disintegration,  13. 
Igneous  rocks,  5. 

Inoculation  of  soil  for  legumes,  138. 
Iron,  proportion  in  earth's  crust,  4. 
Irrigation  for  removal  of  alkali,  120. 

Lacustrine  soils,  described,  25. 

formation  of,  25. 
Law  of  diminishing  returns,  215. 
Legumes,  fertilizers  for,  208. 
Leguminous  plants  as  nitrogen  fixers, 

137. 
"Light"   soil,   and  absolute  specific 
gravity,  35. 

and  apparent  specific  gravity,  38. 
Lime,  absorption  by  soils,  188. 

as  a  soil  amendment,  187. 

caustic  vs.  ground  limestone,  191. 

demonstration  of  flocculation  by, 
194.. 

effect  on  bacterial  action,  189. 

effect  on  plant  diseases,  190. 

effect  on  tilth,  189. 

fineness  of  grinding  limestone,  191. 

forms  of,  189. 

in  relation  to  structure,  42. 

liberation  of  plant-food  materials, 
190. 

magnesium,  190. 

proportion  in  earth's  crust,  4. 

requirements  of  soils,  188. 

tests  for,  193. 
Limestone,  effect  of  fineness  of  grind- 
ing, 191. 

ground  vs.  caustic  lime,  191. 

losses  during  soil  formation,  15. 
Limiting  factors  in  plant  growth,  215. 
Loess,  composition,  27. 

distribution,  26. 

Magnesia,  proportion  in  earth's  crust, 

4. 
Manure,  cow,  partial  composition  of, 

222. 
effect  of  food  on  composition  of, 

224. 


252 


INDEX 


Manure,  farm,  221. 

farm,    agricultural    evaluation    of, 
226. 

farm,  an  unbalanced  fertilizer,  223. 

farm,  application  to  land,  231. 

farm,  chemical  composition  of,  222. 

farm,    commercial    evaluation   of, 
225. 

farm,  covered  barnyard  for,  230. 

farm,  deterioration  of,  226. 

farm,  experiments  with,  233. 

farm,  fermentations  of,  227. 

farm,  leaching  of,  227. 

farm,  methods  of  handling,  230. 

farm,  place  in  crop  rotation,  231. 

farm,  protected  more  effective,  228. 

farm,  reinforcing,  229. 

farm,  solid  and  liquid,  221. 

green,  crops  used  for,  238. 

green,  materials  supplied  by,  236. 

green,  handling,  240. 

green,  nature  of,  235. 

green,  protective  action,  235. 

green,  when  to  use,  239. 

horse,  partial  composition  of,  222. 

quantities  voided  by  animals,  224. 

sheep,  partial  composition  of,  222. 

swine,  partial  composition  of,  222. 

value  from  different  animals,  225. 
Marine  soils,  composition  of,  24. 

described,  24. 

distribution  of,  24. 

formation  of,  24. 
Mechanical  analysis  of  soil,  31. 

determination  of  class  from,  34. 

method  for,  46. 

of  some  typical  soils,  32. 

relation  of  crops  to,  32. 

size  of  separates,  32. 
Mechanical   composition   of   various 

soil  classes,  34. 
Metamorphic  rocks,  5. 
Minerals,     from     which    rocks    are 
formed,  6. 

soil-forming,  laboratory  exercise,  8. 

plant-food  materials  in,  7. 

relation  to  soil,  6. 
Moisture,  see  water. 
Muck,  origin,  21. 

relation  to  lime  and  potash,  22. 
Mulch,  depths  of,  75. 


Mulch,  effectiveness  of,  75. 

frequency  of  stirring,  74. 

of  soil,  nature  and  use,  74. 
Mulches,  for  moisture  control,  74. 

test  for  conservation  of  water  by, 
87. 

Nitrate  formation,  depths  of  occur- 
rence, 135. 

effect  of  aeration  on,  132. 

effect  of  lime  on,  189. 

effect  of  sod  on,  134. 

effect  of  temperature  on,  133. 
Nitrate  of  soda,  effect  on  soils,  159. 

sources  and  composition,  157. 
Nitrates,  as  plant-food  material,  156. 

crops  markedly  benefited  by,  158. 

loss  in  drainage  water,  135. 

test  for,  in  soil,  140. 
Nitrification,  132. 

Nitrogen,   animal   products  contain- 
ing, 163. 

availability  in  fertilizers,  166. 

effects  on  plant  growth,  165. 

fixation,  nature  of,  136. 

fixation  by  free  living  germs,  139. 

fixation  by  plants,  137. 

forms  in  fertilizers,  157. 

forms  in  which  used  by  plants,  156. 

in  fertilizers,  155-170. 

in    soils,    quantities    of    different 
forms,  155. 

organic,      direct      utilization      by 
plants,  156. 

organic,  fertilizers  containing,  162. 

vegetable  products  containing,  163. 
Nodules,  examination  for,  142. 

on  leguminous  plants,  137. 

Orchards,  fertilizers  for,  209. 
Organic  matter,  and  drainage,  53. 

and  formation  of  acids,  55. 

and  nitrogen,  54. 

and  plant-food  material,  54. 

and  soil  color,  53. 

and  soil  organisms,  54. 

benefits  of,  52. 

effect  on  structure,  41. 

effect  on  availability  of  plant  nu- 
trients, 102. 

estimation  of,  58. 


INDEX 


253 


Organic  matter,  examination  of  soil 
for,  58. 

extraction  of,  59. 

influence  on  rate  of  percolation,  59. 

influence  on  water  held  by  soils,  60. 

injurious  effect,  55. 

in  soil,  description,  51. 

in  soil  management,  55. 

kinds  of,  51. 

porosity  of,  53. 

sources  of,  57. 
Oxygen,  proportion  in  earth's  crust,  4. 

Packing,  subsurface,  78. 
Particles  of  soil,  examination,  46. 

number  per  gram,  30. 

relative  sizes,  31. 

shape  of,  30. 

space  occupied  by,  30. 
Peat,  origin,  21. 
Percolation,  test  for  rate  of,  86. 
Plant  constituents,  obtained  from  air 
or  water,  3. 

obtained  from  soil,  3. 
Plant-food   materials,   available  and 
unavailable,  94. 

essential  to  growth,  3. 

absorption  by  plants,  105. 

in  apatite,  7. 

in  calcite,  7. 

in  drainage  water,  102. 

in  dolomite,  7. 

in  farm  manure,  222. 

in  green  manures,  236. 

in  gypsum,  7. 

in  hematite,  7. 

in  liquid  excreta,  222. 

in  minerals,  7. 

in  soils,  90. 

in  solid  excreta,  222. 

laboratory  exercise,  9. 

liberation  by  lime,  190. 

movement  of,  93. 

obtained  from  air  or  water,  3. 

obtained  from  soil,  3. 

possible  exhaustion,  109. 

proportion  in  soils,  93. 

quantities  in  earth's  crust,  4. 

removed  by  crops,  108. 

total  supply  in  soils,  92. 

variations  in  soils,  90. 


Plan*  growth,  conditions  of,  labora- 
tory exercise,  9. 
Plant  nutrients,  laboratory  exercise, 

9. 
Plant  roots,   aid  in  solution  of  soil 
constituents,  106. 
solvent  action,  107. 
Plants,  effect  on  rock  disintegration, 
14. 
substances  essential  to  growth,  3. 
uses  of  water  by,  2. 
Phosphate,  bone,  171. 

mineral,  171. 
Phosphoric    acid,     effect    on    plant 

growth,  175. 
Phosphoric  acid,  plants  benefited  by, 
176. 
proportion  in  earth's  crust,  4. 
reverted,  173. 
Phosphoric  acid  fertilizers,  171. 

availability  of,  174. 
Pore  space,  its  determination,  49. 

relation  to  structure,  37. 
Potash,  effect  on  plant  growth,  181. 

proportion  in  earth's  crust,  4. 
Potash  fertilizers,  sources,  179. 

wood  ashes,  180. 
Province,  the  soil,  in  soil  survey,  44. 

Quartz,  substance  of  which  composed, 

7. 

Residual  soils,  composition,  20. 
described,  18. 
distribution  of,  20. 
loss  during  formation,  19. 
Rock,  changes  in  soil  formation,  15. 
disintegration  by  heat  and  cold,  12. 
disintegration,   effect  of  gases  on, 

14. 
disintegration,  effect  of  glaciers  on, 

13. 
disintegration,  effect  of  ice  on,  13. 
disintegration,  effect  of  plants  on, 

14. 
erosion  by  wind,  14. 
expansion  by  heat,  12. 
relation  to  soil,  15. 
Rocks,    from    which    soil    has    been 
formed,  5. 
igneous,  5. 


254 


INDEX 


Rocks,  losses  during  soil  formation,  15. 

metamorphic,  5. 

sedimentary,  5. 

soil-forming,  laboratory  exercise,  9. 
Rolling  land,  78. 
Root  crops,  fertilizers  for,  209. 
Root  systems  of  different  crops,  243. 
Roots  of  plants,  effect  on  structure, 

41. 
Rotation  of  crops,  242. 

and  soil  productiveness,  242. 

management  of,  246. 

nutrients  removed  by,  243. 

Sedentary  soil,  18. 
Sedimentary  rocks,  5. 
Separates  of  soil,  32. 

chemical  composition  of,  36. 
examination,  46. 
properties  of,  35. 
Series,  the  soil,  in  soil  survey,  44. 
Soil,    as    a    mechanical    support    for 
plants,  1. 
as  a  reservoir  for  water,  2. 
as  a  source  of  plant-food  material, 

2. 
changes    during     formation    from 
rock,  15. 
Soil  class,  in  classification  for  surveys, 
44. 
method  lor  its  determination,  47. 
Soil  formation,    agencies   concerned, 
11. 
and      transportation,      laboratory 
exercise,  17. 
Soil  formations,  1,  18. 
Soil-forming      minerals,      laboratory 

exercise,  8. 
Soil-forming   rocks,  laboratory  exer- 
cise, 9. 
Soil  mulch,  nature  and  use,  74. 
Soil   province,    in    classification    for 

surveys,  44. 
Soil,  relation  to  rock,  15. 
Soil  series,  in  classification  for  sur- 
veys, 44. 
Soil  survey,  described,  43. 
classification  of  soil  for,  43. 
information  furnished  by,  44. 
Soil  type,  in  classification  for  surveys, 
44. 


Soils,  residual,  18. 

sedentary,  18. 

transported,  18. 
Specific  gravity,  apparent,  its  deter, 
mination,  48. 

of  soil,  apparent,  38. 

of  soil  particles,  absolute,  35. 

of  soil  particles,  apparent,  38. 
Structure,  of  soil,  as  affected  by  freez- 
ing and  thawing,  40. 

as  affected  by  lime,  42. 

as  affected  by  organic  matter,  41. 

as    affected    by    plant    roots    and 
animals,  41. 

as  affected  by  tillage,  42. 

as  affected  by  wetting  and  drying, 
40. 

conditions  that  affect,  39. 

granular  or  crumbly,  37. 

defined,  37. 

relation  to  pore  space,  37. 

relation  to  texture,  39. 

relation  to  tilth,  39. 

operations  that  affect,  39. 

separate  grain,  37. 
Subsurface  packing,  78. 
Sulfate    of    ammonia,    action    when 
applied  to  soils,  160. 

composition,  160. 

sources,  159. 
Sulfur,  as  a  fertilizer,  182. 

contained  in  crops,  182. 

contained  in  drainage  water,  183. 

contained  in  fertilizers,  184. 

contained  in  soils,  183. 

proportion  in  earth's  crust,  4. 

Temperature,  control  of,  151. 

demonstration  of  effect  of  slope  on , 
154. 

factors  that  modify,  150. 

of  soil  and  atmosphere,  149. 

of  soils,  relation  to  plant   growth, 
148. 
Texture,  of  soil,  described,  30. 

relation  to  crops,  32. 

relation  to  structure,  39. 
Tile,  concrete,  81. 

drains,  81. 

laying,  83. 
Tillage  in  relation  to  structure,  42. 


INDEX 


255 


Tilth,  as  affected  by  lime,  189. 

in  relation  to  drainage,  79. 

relation  to  structure,  39. 
Toxic  substances  and  crop  rotation, 

246. 
Transpiration,    as    affected    by    soil 
moisture,  69. 

by  different  crops,  69. 

conditions  affecting,  70. 

ratio,  69. 

relation  to  soil  fertility,  70. 

test  for  loss  by,  88. 
Transported  soil,  18. 
Type,  the  soil,  in  soil  survey,  44. 

Vegetables,  fertilizers  for,  209. 

Water,  as  a  soil  transporting  agent, 
13. 

capillary,  capacity  of  soils,  63. 

capillary,  definition,  62. 

capillary,  effect  of  structure  on 
movement  of,  65. 

capillary,  effect  of  texture  on 
movement  of,  65. 

capillary,  height  of  column  and 
movement,  66. 

capillary  movement  and  plant  re- 
quirement, 71. 

capillary,  movement  of,  64. 

capillary,  properties  of,  63. 

carrying  power  for  rock  debris,  13. 

control  of  soil  content,  72. 

effect  on  rock  disintegration,  12. 

evaporation  from  soil,  73. 


Water,  expansive  power  in  freezing, 
12. 

forms  in  soils,  61. 

gravitational,  definition,  62. 

gravitational,  movement,  67. 

gravitational,  properties  of,  66. 

hygroscopic,  definition,  61. 

hygroscopic,  properties  of,  62. 

in  soil,  determination  of  per  cent, 
85. 

optimum  content  for  plant  growth, 
71. 

percolation  through  soil,  73. 

quantity  required  to  mature  a  crop, 
70. 

relation  to  plants,  67.    - 

requirements  of  plants,  68. 

run-off,  72. 

solvent  action  on  rock,  12. 

test  for  capacity  of  soil  for,  87. 

test  for  capillary  movement,  86. 

test  for  conservation  by  mulch,  87. 

test  for  loss  by  transpiration,  88. 

test  for  rate  of  percolation,  86. 

uses  by  plants,  2. 

ways  in  which  useful  to  plants,  68. 
Water-soluble  matter  in  soil,  96. 

test  for,  111. 
Water  table,  67. 

Weeds  that  flourish  on  acid  soils,  115. 
Wetting  and  drying  soil,   affect  on 

structure,  40. 
Wind,  action  in  transporting  soil,  14. 

erosive  action  on  rocks,  14. 
Windbreaks,  to  decrease  evaporation, 
78. 


Printed  in  the  United  States  of  America. 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 

AN  INITIAL  FINE  OF  25  CENTS 

mmmm 


NOV  131940 


— mv-±^m 


[N0V15  1941 


-g#*et^- 


?<>1  *  D 


LD  21-l00m-8,'34 


YB  51414 


y 


454794 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


